Rock Hound Guide to Agate & Jasper

Crystalline & Cryptocrystalline Quartz

2011-04-19T11:28:00.000-07:00

Quartz (SiO₂) [Agate, jasper, chalcedony]

Quartz crystals (clockwise from bottom left). Transparent hexagonal
quartz crystals capped by a hexagonal pyramid from Hot Springs,
Arkansas, smoky quartz from the State Line, Wyoming, amethyst,
translucent quartz, and bottom right, smoky quartz from Big Creek, WY.

When we discuss quartz, chalcedony, agate and jasper, we are talking about the same material. All are formed of silica (SiO₂) and each is different from the other only because of crystallinity or color. For example, quartz is the most common constituent of the earth’s crust and when found in veins, it can be coarse crystalline with distinct crystals or massive with no distinct crystals - most often it is massive.

When we speak of massive we mean that we cannot distinguish any distinct crystal form with the naked eye - and this is typical of rock quartz, jasper and agate. When found in hand specimen, this could be termed simply massive quartz, quartz, rock crystal or chalcedony.

If the quartz is found in crystalline form, something that is attractive to mineral collectors, rock hounds, and new-age crystal healers, the quartz often occurs as hexagonal (6-sided) prisms that are almost always capped by a hexagonal pyramid.

Less commonly, quartz is found as doubly terminated crystals. This means the quartz crystal has distinct hexagonal prisms at both ends of the crystal. By the way, I met a person years ago who had a round tower in their house filled with quartz crystals for healing. Scientifically, there is no way that quartz can heal a person unless it is psycho-somatic – it is like putting your trust in a politician not to spend your money (although this may not be a good analogy as there is plenty of proof that politicians contantly rob tax-payers – it called an election). Quartz is typically found as (1) rock crystal, (2) amethyst, (3) citrine, (4) smoky, (5) rose, (6) chatoyant quartz, or (7) crystalline quartz.

Milky quartz vein (massive quartz) in Mary Ellen gold mine,
WY. When this rock weathers out, it forms massive pieces of
quartz referred to as rock crystal.

Hardness

7.0 (Mohs Scale). This is just a little harder than your car’s windshield – this is why it gets so pitted if you live in areas with blowing sand like Arizona.

Color

Quartz is found in a multitude of colors that include colorless, white, red, orange, yellow, gray, brown, black, lavender, violet, purple, pink, blue or green. Essentially every color is seen in quartz.

In its chemically pure form, quartz is usually colorless or white. As with other gemstones, small amounts of chemical impurities produce a variety of colors. Quartz with impurities is quite common, and the range of possible colors spans the spectrum.

In its various valence states, iron produces many colors in quartz, the most important being the purple to red-violet of amethyst and the lemon-yellow of citrine. Iron is also responsible for reds, yellows and browns typical of many agates. Iron gives carnelian and jasper their brownish-reds and oranges. Iron or manganese produces browns and blacks in dendritic agates. Traces of titanium cause the characteristic pink of rose quartz and nickel gives chrysoprase its apple-green color (Schumann 1997). Other chemical colorants are possible. Mineral inclusions in coarsely crystalline quartz and in cryptocrystalline varieties may also impart colors as well as optical effects such as chatoyancy.

Specific Gravity – 2.65 (more than twice as heavy as water).

Cleavage – Generally none. In other words, you are not going to be able to break quartz along distinct planes like you would diamond. If you do strike quartz with a chisel and hammer to try to cleave, it will break forming conchoidal fracture (just like broken glass).

This reminds me of a family from Cheyenne who visited my office at the University of Wyoming thinking they had found the largest diamond on earth that was the size of a football. They apparently had been told by a gemologist in Cheyenne that it was a diamond, but needed to have it verified by someone else (now that was a very good suggestion). When they brought it into my office, I knew immediately it was rock crystal, but I wanted to let them down slowly. So I toyed with them a little bit and then got out a diamond chip and cut the quartz with little effort. They were visible disturbed I would dare scratch the diamond that would pay for their mansions and allow their off-spring live a life of luxury. After I pointed out that if it was diamond, I would have had a very difficult time cutting the stone, they forgave me and left.

BUT – they were not done. On our staff, we had a super person who contributed to geology and to the Laramie community, but he was somewhat of a klutz. Ray unfortunately ran into some of the more disgusting politicians in Wyoming who drove him to the suicide clinic a few years later. Anyway, Ray was a very good field geologist, but he was not so good at mineralogy. A few weeks later, this same family came back to the university and asked to see Ray and avoided me. Ray told me what was going on and I said he should go ahead and give these people a third opinion. What these people didn’t know was that Ray had no experience with diamonds. During this gathering, Ray told the family he wanted to look at the Rock Crystal a little closer. As he was carrying the stone to this lab, he dropped it. I wish I could have seen everyone’s expressions – it would have been priceless. Here was a diamond much larger than the 3,106 carat Cullinun (the largest diamond ever found), and it was dropped on the floor shattering into dozens of pieces. Ray’s response simply was, “well, it has conchoidal fracture, so it’s not a diamond”. Ray was partially right.

Group of agates

Diamonds also have conchoidal fracture, but if it were a diamond and was dropped on the floor, it would have produced pieces with conchoidal fracture as well as pieces with flat, smooth, cleavage planes. But it didn’t matter. This was just another piece of rock crystal – one of many that I examined over the years brought in by prospectors.

Crystal System & Habit – Trigonal, hexagonal-rhombohedral. The common habit of quartz is anhedral (formless) masses and well-formed hexagonal prisms capped by one or two hexagonal pyramids or terminated by rhombohedra.

Luster –vitreous

Electrical – Strongly piezoelectric and pyroelectric.

Mineralogy

Crystal Habit. Quartz crystallizes in the trigonal system (Berry and Mason, 1968; Hausel 1986, 2005, 2009; Kievlenko, 2003;). Coarsely crystalline quartz most often is found as anhedral grains and masses in various rock types. Large crystals usually form singly terminated hexagonal prisms that are often striated perpendicular to the c-axis (the c-axis is an optic axis that is parallel to the hexagonal prism) and are capped by a pyramid or rhombohedra. Such prisms typically range from microscopic to crystals weighing several hundred pounds. Periodically, doubly terminated prisms are found that are bipyramidal, but these are less common (Mason and Berry, 1968).

Amethyst typically is dominated by forms with rhombohedral faces, whereas prism faces are absent, or at best, poorly developed. This habit is typical of crystals that have grown simultaneously on the walls of open cavities (Lowell and Koivula, 2004).

Twinned quartz -
note smaller crystal
growing from larger.

Twinning. Quartz crystals are sometimes twinned with two different crystals growing together.

Size. Crystals usually vary from microscopic to specimens weighing several hundred pounds. On the extreme end, rock crystals have been found that weigh many tonnes (Schuman 1997). Pyramidal amethyst crystals up to 10 inches in diameter are reported from the vicinity of Thunder Bay, Ontario, although facetable gem material is usually only found within a small portion of such large crystals (Kievlenko 2003).

Fluorescence. Quartz is not fluorescent or luminescent (Hurlbut and Switzer 1979).

Geochemistry – Quartz (SiO₂) is the most common rock-forming mineral in the earth’s crust and occurs in both coarsely-crystalline and microcrystalline forms. In pure form, it is composed of 46.7% silicon and 53.3% oxygen (Bauer 1968; Hurlbut and Klein 1977). Quartz is usually very pure SiO₂ (Mason and Berry 1968; Hurlbut and Klein 1977). Quartz is infusible, and generally considered insoluble except in hydrofluoric acid (Bauer 1968; Hurlbut and Klein 1977). However, Deer, Howie, and Zussman (1971) note that the presence of either NaOH or NaCl in water accelerates both solution and crystallization of quartz by several orders of magnitude over that of pure water, which has ramifications relating to its geological occurrence.

Mineral Associations & Inclusions

Quartz, being a common constituent of many rock types, is found in association with a wide variety of minerals. These include feldspar, muscovite, biotite, chlorite, tourmaline, beryl, hematite, iolite, barite, fluorite, nephrite jade, gold, sulfides and others too numerous to mention (Ford 1949; Bauer 1968; Keller 1990; Hausel and Sutherland 2000; Garland 2004). Many of these associated minerals often occur as inclusions within quartz. The diversity of the inclusions is a striking feature of quartz (Gübelin and Erni 2000). The introduction of silica-rich fluids into the presence of other minerals may be responsible for some inclusions, or the foreign inclusions may crystallize somewhat simultaneously with the quartz. Many of the better-known inclusions give rise to type names that are often listed as subspecies of gem quartz.

Reddish-brown hematite flakes, or more commonly flakes of green fuchsite mica produce the glittery metallic appearance (aventurescence) and colors characteristic of the coarsely crystalline quartz variety known as aventurine (Schumann 1997). Rutilated quartz (quartz containing elogated mineral inclusions of rutile needles) most commonly exhibits yellowish-brown to golden-yellow colors, but also has produced coppery-red and silver-gray colors. Although rutile in quartz is relatively common, rutile in highly transparent quartz is rare. The abundance and parallel alignment of fine acicular rutile inclusions sufficient to produce chatoyancy in transparent quartz is rare (Koivula and Tannous 2004a).

Beautiful slab of banded agate from the Jay Sundberg
collection, Rawlins, Wyoming.

Gold has always been associated with quartz to the degree that early prospectors almost always looked for quartz in their search for the precious metal. Gold in quartz, most commonly in milky quartz, is cut and polished in a variety of shapes and sizes, primarily for use as jewelry. Striking specimens of gold-in-quartz have been produced from the Badger mine, Mariposa County, California, from the Sixteen-to-One mine in Sierra County, California, and from Australia (Laurs 2005c).

Less commonly found within quartz include covellite, which produces an electric pink schiller in both smoky and colorless quartz (Quinn and McClure 2005), and pezzottaite (a Cs-, Li-rich member of the beryl group) that shows as a pink-zoned inclusion in colorless quartz (Koivula and Tannous 2005). Koivula, Tannous, and DeGhionno (2004) reported colorless quartz appears blue due to the copper content of abundant ajoite fibers, strawberry-red due to numerous transparent to translucent hematite inclusions, and green due to nickel content of included népuoite. Lead-gray metallic molybdenite inclusions have been found within large rock crystals recovered from the Confianza mine, Chile (Koivula and Tannous 2004d). Well-formed graphite cylinders and botryoidal masses have been found in rock crystal in Brazil (Hyrsl 2004b).

Gas-fluid inclusions are common in quartz (Bauer 1968). Most are microscopic, but large visible ones also occur. Analysis of gas-fluid inclusions provides a wealth of information about the pressure, temperature, and chemical environment under which quartz crystallized. Such inclusions are always present in amethyst with the greatest abundance near the base of the crystal. These are primarily formed of gaseous and liquid carbonic acids (Kievlenko 2003). Carbon dioxide, water, and common salt are also found as inclusions (Bauer 1968), as are natural petroleum fluids, gases, and solids (Koivula and Tannous 2004b).

Quartz crystals hosting both fluid and solid natural petroleum inclusions were reported by Koivula and Tannous (2004b) in Baluchistan, Pakistan. Yellow to brownish-yellow and clear fluid inclusions generally consist of natural petroleum, methane gas, and water. A yellow to orange or blue luminescence under long-wave ultra-violet light is characteristic of fluid petroleum inclusions. The darker bituminous, brown to black amorphous solid petroleum-derived materials are referred to as asphaltite. Doubly-terminate quartz crystals from Herkimer County, New York have been known to host amorphous asphaltite hydrocarbons as inclusions. These originate within silicified dolomites, and appear to have developed during digenesis of the host rock. Hydrocarbon inclusions are also abundant in Sichuan Province, China, but the Herkimer rock crystals are the best known (Hyrsl 2004).

Varieties

Rock Crystal. Rock crystal is essentially colorless quartz. Because of its low refractive index (the amount of light that is broken up to produce fire or a rainbow of colors) and glassy appearance it is seldom used as a gemstone. It exhibits characteristics similar to those of synthetic glass – thus it has few properties that would make it attractive for adornment. Even so, colorless raw quartz crystals are periodically used in earrings and necklaces due to the characteristic hexagonal prisms that are visually interesting. Beautifully crystallized quartz crystal prisms are attractive for museums and collectors. The recent nonscientific practice of crystal therapy has resulted in increased interests in quartz crystals along with increased prices.

Amethyst in ring

Amethyst. Amethyst is colored quartz that ranges from mauve to deep violet. The coloring agent for amethyst is small amounts of Fe³⁺ that is distributed in the crystal structure in layers typically parallel to the rhombohedral faces. Thus in many cut stones clear bands of quartz may be seen alternating with colored bands (Hurlbut and Switzer 1979). Amethyst has been one of the more popular gemstones throughout history and is even mentioned in the Bible as one of 12 sacred stones. It is generally considered the most valuable of all the quartz gemstones.

Gems of similar color were once included together in a single group centuries ago, such as amethyst and sapphire. This is the origin of the term oriental amethyst that has been applied to similar colored sapphire. The color in amethyst can be modified through heat treatment. At temperatures of 250 to 350^oC, the stone will become colorless; however, the color is restored by radioactive irradiation. At higher temperatures (450 to 500^oC) the color is irreversibly damaged and the mineral may take on a reddish-brown to yellow-citrine color. The violet color seen in amethyst will form following radioactive bombardment (ionization) causing trace iron in the crystal to lose an electron and change from trivalent to the tetravalent state. Higher-temperature thermal heating will destroy both Fe³⁺ and Fe²⁺ centers in the quartz yielding a greenish to yellowish color in the crystal (Kievlenko 2003). In nature, amethyst is thought to have a hydrothermal genesis.

Citrine. Citrine is a pale- to dark-yellow, brownish-yellow, or honey-yellow quartz with a russet tint named after its resemblance to citrus lemons. It has been mistaken for topaz particularly in the ancient past and has erroneously been given additional names such as ‘topaz quartz’. Even so, citrine can be distinguished in both the faceted and natural form from topaz by index of refraction and specific gravity. In hand specimen, the crystal habit and cleavage is used to distinguish one from the other. Cipriani and Borelli (1986) report that the specific gravity for citrine (and feldspar gems) are the lowest for yellow, transparent gemstones, whereas topaz is noticeably higher. The luster is slightly inferior to topaz and topaz may show signs of incipient cleavage that would be non-existent in the citrine.

Wiggins Fork citrine, Wyoming

The coloring agent for citrine is iron. Citrine can be produced by heat treatment of amethyst at high temperatures. Almost all citrines derived in this manner will have reddish tint that tends to contrast with the predominant pale-yellow in most natural citrines (Schumann 1997). According to Hurlbut and Switzer (1979), heat treated citrine will exhibit color banding typical in amethyst and lack slight pleochroism seen in natural citrine. In contrast, Cipriani and Borelli (1986) report that natural citrine exhibits patches and color bands similar to amethyst, although the zoning in citrine is less obvious. Citrine exhibits a nice vitreous luster and is generally free of mineral inclusions.

Smoky Quartz. Smoky quartz varies from black to brown to smoky yellow and grades into citrine. The dark color of smoky quartz is thought to be the result of radioactive damage during exposure to radiation. Upon heating, smoky quartz will turn colorless, and will return smoky upon exposure to radiation. Rutile needles are common inclusions in smoky quartz (Schumann 1997). The best-known locality is that of the Swiss Alps, where veins have yielded many tons of beautiful crystals. Other notable localities are Russia, Brazil, Madagascar, and Scotland. In the US, smoky quartz has been reported in the Pikes Peak region of Colorado, and at various localities in Maine and New Hampshire.

Rose quartz

Rose Quartz. Rose quartz often occurs as coarse-crystalline anhedral quartz that varies from pale pink to deep rose-red, which often fadesupon exposure to sunlight. Rose quartz is seldom transparent and instead is turbid. Its color is thought to be due to the trace titanium. In some rose quartz, microscopic needles of rutile are found that are oriented in three directions at 120^o from one another and at right angles to the c-axis. When manufactured into a cabochon with proper orientation, the mineral will produce a distinct 6-rayed star due to light being reflected from the rutile needles.

Chatoyant Quartz. There are several minor ornamental stones of chatoyant quartz. Such quartz contains parallel fibrous mineral inclusions that exhibit wavy reflections as they are rotated in light (Hurlbut and Klein 1977). Rather than fibrous mineral inclusions, Koivula and Tannous (2004c) associate chatoyancy with “thin hollow tubes resulting from growth blockage (growth tubes) and/or post-growth dissolution features (etch tubes)”. Chatoyancy is also seen in Tiger’s Eye, a variety of cryptocrystalline quartz.

Cryptocrystalline Quartz (Chalcedony)

Cryptocrystalline quartz includes many varieties of ordinary chalcedony as well as the extraordinary agate, carnelias, chrysoprase, onyx, sard, jasper, chert and flint that are so loved by lapidaries and rock hounds.

Mineralogy

Physical Properties

Crystal Habit. Cryptocrystalline quartz crystallizes in the trigonal system and is separated into two types: (1) fibrous and (2) granular. These two may occur in the same deposit and grade into each other. Although the characteristics of each are often quite distinct, in many stones the differences are indistinguishable without the aid of a powerful microscope (Hurlbut and Switzer 1979). Chalcedony consists of microscopic fibrous quartz crystals with minute pore spaces that may be filled with water or air. The pore spaces may also contain minute particles of other minerals that produce that attractive coloring and banding in some agates (Sinkankas 1975). The granular type is made up of roughly equidimensional rather than fibrous microcrystals and includes jasper, flint, and chert (Hurlbut and Switzer 1979). The distinction between fibrous and granular cryptocrystalline quartz is not universally recognized and the two types are often lumped together as chalcedony (Schumann 1997).

Silicified ironstone concretions with distinct coarse
botryoidal habit. Photo by Wayne Sutherland.

The most common granular varieties of cryptocrystalline quartz are flint (dark-brown to almost black due to impurities) and chert (commonly opaque light gray to white). The two grade into one another and both have dull luster. Although these were used extensively by early man for tools, today these have very limited use as a semi-precious gem. Jasper, also granular, is typically deep red, reddish-brown to yellow-orange due to the presence of traces of iron oxide within jasper. Jasper is almost opaque and has a dull luster (Hurlbut and Switzer 1979) and is commonly used as a low-value ornamental stone or lapidary semi-precious stone.

Fibrous cryptocrystalline chalcedony commonly forms botryoidal masses with fibers oriented perpendicular to the hummocky surface. Chalcedony also occurs as cavity and void fillings or linings in various rock types. It is also found as fracture fillings and as replacements of organic material such as petrified wood. Wide variations in color, banding and patterns of inclusions are the source of the prolific names of subvarieties of chalcedony (Hurlbut and Switzer 1979).

Cleavage and fracture. Pure chalcedony has no cleavage and breaks with uneven rough to splintery, or conchoidal fracture similar to glass (Sinkankas 1959; Bauer 1968; Schumann 1997).

Hardness. The hardness of chalcedony is typically listed as 7 on the relative Moh’s hardness scale. However, some sources such as Schumann (1997) indicate that its hardness will range from 6.5 to 7.0 and Bauer (1968) reports its hardness to be 6.5. Sinkankas (1959) explains that the hardness may appear to be lower depending on its porosity and purity as related to its fibrous structure.

Specific gravity. The specific gravity of chalcedony is 2.58 to 2.64. This is slightly lower than coarsely crystalline quartz because of its slight porosity (Sinkankas 1959; Hurlbut and Switzer 1979).

Size. Chalcedony can vary in size from small grains to large masses weighing tons.

Optical Properties

Color. Pure chalcedony is pale blue to white to pale gray, with other colors caused either by chemical impurities or by mineral inclusions (Sinkankas 1959; Schumann 1997).

Fluorescence/Piezoelectricity. Chalcedony has no reported piezoelectric properties. Pure chalcedony is fluorescent blue to white, whereas fluorescence in other varieties ranges from nonexistent to strong yellow to blue-white depending on the presence of chemical impurities or mineral inclusions (Schumann 1997). Some of the popular Sweetwater moss agates from the Granite Mountains in central Wyoming fluoresce brilliant yellow due to presence of hydrous uranium arsenate (Hausel and Sutherland, 2000).

Index of Refraction, transparency, pleochroism. The refractive index for cryptocrystalline quartz is about 1.53 (Hurlbut and Switzer, 1979). Sinkankas (1959) shows the refractive indices for chalcedony at 1.533 and 1.539, and Schumann (1997) states a range for pure chalcedony of 1.530 to 1.540, with a slight double refraction up to 0.004 with no dichroism. Pure chalcedony is translucent to transparent with a waxy to dull luster, but may vary to almost opaque with mineral inclusions (Sinkankas, 1975; Schumann, 1997).

Chatoyancy. Chatoyancy is displayed in some varieties of chalcedony.

Adularescence. Adularescence is rare in chalcedony. However, violet adularescent chalcedony is described in specimens that were found in Iran by Douman and Quinn (2004).

Varieties of Chalcedony (agate, jasper, onyx, chrysoprase)

Agate. Chalcedony nodules with banded colors (other than red, brown to yellow) are typically referred to as agates. The color bands tend to parallel the outsides of the nodules, or may form horizontal layers within the nodules. These derive from their formation as cavity linings and fillings in a variety of host rocks. The banding is usually distinct; however, common usage applies the name agate to varieties of chalcedony that also show no banding, such as moss agate (Sinkankas 1975). Thus, agate generally refers to the lighter-colored chalcedonies, whether banded or homogeneous.

Mass of botryoidal agate breccia
known as Youngite

Many descriptive or local names have been applied to agates (Sinkankas 1959 and 1975; Mason and Berry 1968; Schumann 1997). A short list of a few of these includes:

banded agate – an agate that exhibits distinct color banding.
fortification agate – an agate with banding that flows outward into several points within a nodule to provide the appearance similar to a medieval fortress.
eye agate – an agate with concentric banding surrounding a point in the center that gives the appearance of an eye.
agate breccia – an agate formed of broken broken lithic fragments that is rehealed by chalcedony and or quartz.
moss agate - a translucent chalcedony that encloses moss-like manganese or iron oxide dendrites.

Cut and polished Youngite agate
breccia

botryoidal agate – agate that exhibits botryoidal texture. An external hummocky to rounded form similar to bunches of grapes.
dendritic agate - moss agate that exhibits a distinct dendritic pattern.
flame agate - a dendritic agate with red to orange flame-shaped dendrites
iris agate – an agate that exhibits a spectral display of colors due to microscopic diffraction grating caused by alternating bands of material that has higher and lower refractive indices.

There are many other varieties of agates that are provided local names, such as youngite (pink to cream limestone breccia clasts rehealed with bluish-gray chalcedony and drusy quartz, from Hartville area, southeastern Wyoming) or the previously mentioned Sweetwater moss agates (Hausel and Sutherland, 2000). Others such as the Fairburn agate in South Dakota is a popular agate that is a banded agate.

Bloodstone. Bloodstone is a green opaque chalcedony (or agate) with red spots. It is also known by the earlier Greek name, heliotrope (Mason and Berry 1968; Hurlbut and Klein 1977; Schumann 1997).

Carnelian. Translucent red to orange-red and brownish-red chalcedony that is colored by hematite is known as carnelian. Carnelian grades into sard and is similar to jasper, in fact; many specimens of carnelian can be cut from many pieces of jasper (see jasper). According to Vanders and Kerr (1967), India is the principal source for carnelian, but other sources include Wyoming, Washington, Colorado and Michigan (Hausel, 2009).

Chrysoprase. An apple-green to light-turquoise green chalcedony often colored by garnierite, a nickel silicate (Sinkankas, 1975). It is a secondary mineral that often forms in veins in nickel-rich host rocks such as serpentinite. Two localities in the US where chrysoprase has been identified include Riddle, Oregon and Tulare County, California (Hausel and Sutherland, 2006).

Jasperoid Onyx discovered by the
author on Quaking Asp Mountain
south of Rock Springs, WY

Onyx. Onyx is made up of alternating dark and light colored straight parallel bands or layers of chalcedony, usually black, white, red, and yellow. A similar appearing onyx is distinguished from onyx chalcedony which is known onyx marble. Onyx marble is considerably softer and easily scratched (Hausel, 1986; 2009). Some excellent onyx marble is found in the northern Hartville uplift of Wyoming (Hausel and Sutherland, 2000).

Petrified wood. Petrified wood, also known as fossilized wood is produced by silica-rich solutions in groundwater replacing buried organic material. The silica-rich solutions are supersaturated in silica and slowly replace organic material in entire plants and trees with silica producing pseudomorphs of the plant that often contains extraordinary details of the original tree all the way down to cellular structure. Cryptocrystalline quartz of many types, including agate and jasper, may be found in petrified wood.

Petrified sequoia tree in Wasatch Fm
near Buffalo, WY (photo from Wayne
Sutherland).

Petrified wood is found on all continents with one of the most spectacular examples being the Petrified Forest National Monument and surrounding areas in northern Arizona where Triassic Shinarump and Chinle Formations contain numerous petrified wood tree trucks scattered all over the surface. Petrified wood is also known in the Eden Valley and Blue Forest areas of southwestern Wyoming, from the Wiggins Fork area in Absaroka Mountains of Wyoming, and from Yellowstone National Park in northwestern Wyoming.

Sard. Sard is chalcedony that is primarily colored by goethite (hydrated iron oxide). It is gradational with carnelian and found in many jaspers. Sard is translucent to nearly opaque and occurs in brown, brownish-red, and brownish-yellow colors (Hurlbut and Switzer 1979; Schumann 1997).

Tiger’s Eye. This agate expresses chatoyancy as a golden yellow color on a brown background. Depending on the background or base color, such agates receive various gemological and rock hound terms. When the background color is greenish-gray or green the gem may be known as cat’s eye quartz. When it is a blue-gray to blue, it is known as hawk’s eye quartz, and a stone with mahogany color base is called bull’s eye quartz. The chatoyancy is usually enhanced in rounded, polished, ornamental stones or cabochons.

Banded iron formation from the Miracle Mile paleoplacer
Note the red bands of carnelian, brown bands of sard and
the extraordinary golden bands of tiger's eye. Photo from
Tom Nissen.

The chatoyancy in tiger’s eye is often cited as being caused by pseudomorphic replacement of asbestos-form minerals such as crocidolite (Hurlbut and Klein 1977; Cipriani and Borelli 1986). Heaney and Fischer (2003) proposed that ‘tiger’s eye’ is developed by a vein-filling process in which crocidolite asbestos fibers are cracked apart and resealed by overgrowths of columnar quartz. The quartz provides a relative hardness, and the crocidolite is responsible for the chatoyance found in tiger’s eye. Both processes may produce chatoyancy in different environments.

Most tiger’s eye comes from South Africa although it also occurs in lesser deposits in California (USA), Australia, India, Myanmar, and Namibia (Schumann 1997). In Wyoming, extraordinary Tigers eye is found associated with banded iron formation near Bradley Peak in the Seminoe Mountains and also is found along the north flank of the Seminoe Mountains in the Tertiary to Recent Miracle Mile gold and diamond paleoplacers (Hausel, 1994, 2009).

Geology & Genesis

Primary Deposits. Quartz is a significant component of many igneous, metamorphic, and sedimentary rocks, as well as quartz veins, quartzites, and sandstones. The modes of formation for coarsely crystalline and cryptocrystalline quartz differ in general, but overlap under low temperature conditions. Coarsely crystalline quartz forms under both magmatic and hydrothermal conditions, but may also form by precipitation from silica-saturated, relatively low temperature hydrous fluids, which is the common mode for the formation for chalcedony. In other cases, desilication of country rocks followed by migration of silica in solution to dilational zones during regional metamorphism is also apparent in places.

Gemology

Quartz is one of the more common rock forming minerals and most quartz has little value as a gemstone, but is considered more as a semi-precious, lapidary, or ornamental stone. Some quartz, because of its crystal habit, color, transparency, or mineral inclusions, may have value as a semi-precious stone, or low-value secondary gem. The best quality macrocrystalline quartz varieties are faceted or kept as specimens, while lower-quality material is made into cabochons. Both coarsely crystalline quartz and chalcedony have been carved, although their brittleness generally negates the extremely delicate type of artwork found in the much tougher jadeite and nephrite. Cryptocrystalline quartz varieties are most often finished as cabochons. The translucent to transparent character of chalcedony combined with its moderate hardness, waxy luster, ability to take a polish, and its wide range of colors make it popular as a low-cost gemstone.

Famous Gemstones & Specimens

Large amethyst crystals and other quartz gemstones are not common; one of the largest amethysts was 10 inches in diameter, and found in Thunder Bay Canada. A similar size amethyst was found in Maraba, Brazil. A cut amethyst in the possession of the British Museum of Natural History weighs 343 carats, and a large Brazilian faceted stone of 1,362 carats is located in the Smithsonian collection (Kievlenko 2003). Some enormous, well-formed common quartz crystals weighing up to 289 pounds have been found in the past (Mattana, Crespi and Liborio 1977) and an extraordinary quartz prism found in Mina Geris, Brazil, weighed more than 3,500 pounds (Anomalous 2003). Some of the more impressive, transparent, colorless quartz including some very large specimens have been recovered in Hot Springs County, Arkansas (US).

Very large, well-formed translucent quartz and some large fluorite crystals were found in the Holy Moses pocket on the Godsend claim located in the Crystal Creek area near Lake George south of Denver, Colorado. The pegmatitic minerals were recovered from a miarolitic cavity in the Pikes Peak batholith. Some of the specimens included smoky and colorless quartz weighing up to 439 pounds (Berry and Fretterd 2003).

Banded onyx agate enclosing geode with crystalline quartz.
Specimen from the Jay Sundberg collection, Rawlins, WY

Deposits

This discussion of deposits here must be considered as only a sampling of a voluminous subject due to the abundance of quartz-family gemstones and their wide-spread occurrences. As such, the focus is on amethyst for coarsely crystalline varieties, and on a few chalcedony occurrences, with emphasis on those from Wyoming. This does not negate the importance of other occurrences, merely a method of providing examples from a catalog that would otherwise run into thousands of pages.

The finest amethysts are produced from Brazil, Uruguay, the United States, Madagascar, Russia, India, Australia and South Africa. Large quantities of citrine are found in Brazil, the United States, Spain and Russia. Rose quartz is mainly recovered from Brazil, the United States and Madagascar. Cat’s eye quartz is produced in Sri Lanka, Burma and Germany (Cipriani and Borelli 1986). South Africa has been an important source for hawk’s eye, tiger’s eye and bull’s eye quartz.

Australia Some amethyst occurs in the northeastern portion of Queensland, in eastern New South Wales, and in the northeastern and central portions of Victoria. The amethyst from the Mount Phillips deposit 360 km northeast of Canarvon in Western Australia, occurs in a dike of nontronite-tremolite within migmatites and biotite schist xenoliths. The amethyst forms masses of druses weighing up to 50 kg, and some crystals weigh up to 5 kg. The stones typically have a dark violet color with small transparent zones that can be used for gemstones (Kievlenko 2003). Popular specimens of gold in quartz have also been produced from Australia (Laurs, 2005c).

Bolivia Amethyst deposits in Bolivia are found in the Bolivian craton and are structurally controlled in zones of silicification developed along faults that cut Cambrian limestones. The better amethysts have dense, violet color and are extracted with citrine, as well as with colorless and smoky quartz crystals. A popular gem, known by the trade name ametrine, is zoned, bicolor quartz consisting of a mixture of amethyst and citrine. Some amethyst and quartz is also found in Proterozoic crystalline rocks in breccias and veins (Kievlenko 2003).

Brazil. Brazil produces much of the world’s quartz gemstones and has done so since their discovery there in the 19^th century. Brazil leads the world in it production of amethyst and other coarsely crystalline quartz varieties (Sinkankas, 1959; Bauer, 1968; Gübelin and Erni, 2000) including crystals with unusual inclusions (Hyrsl, 2004a). Brazil is also a major producer of agate, which often occurs within the same deposits as coarsely crystalline quartz.

Hydrothermal amethyst is hosted by Proterozoic quartzite in the southern part of the State of Bahia in eastern Brazil. The fracture-filling veins include distinct veins, stockworks and cavernous fracture zones that are noted for their massive amethyst and euhedral crystals in cavities. Some veins have been traced for several hundred meters along strike and may exhibit widths of 2 to 3 m (6.4 to 9.6 feet).

The Montezuma deposit is considered the largest of these. Obelisk and prismatic amethyst with transparent caps occur in crystal form up to 20 cm in length (8 inches). The amethyst is found in the veins with kaolinite-illite. At the Fazenda Serra do Salto deposit, amethyst is related to a zone of fracturing in white to pink sericitic bearing quartzites. Rod-like greenish gray quartz with amethyst may be as much as 30 cm (12 inches) in length and may cement the breccia. Much of the amethyst is apparently heat-treated to produce yellow and orange-brown citrine under a trade name of ‘Rio Grande topaz’. At the Grogo do Choch deposit, amethyst is associated with stockworks and solution cavities in quartzite. The amethyst is found in radiating groups of crystals on the walls of fractures and ranges from to 3 to 30 cm (1.2 to 12 inches) in length, and is found in some geodes up to 1 m (3.2 feet) in diameter. Some scepter-terminated amethyst is also found at Grogo do Choch. The scepters sit on milky white to brownish red and translucent prisms.

Well-formed, lustrous graphite cylinders, completely enclosed in quartz, have been found in rock crystal from Bahia. In rare specimens, the graphite is botryoidal. Doubly-terminated crystals up to 3 cm long are common, with some as much as 10 cm. Where the graphite extends to the crystal surface, it has either been replaced by yellowish-brown iron oxides or removed completely, with only a hollow cavity remaining (Hyrsl, 2004b).

Exceptionally fine examples of rutilated quartz have been extracted from the Golconda mine in Minas Gerais (Koivula and Tannous, 2004e). Brazil has been known to have produced rutilated quartz with colors ranging from the more common golden-yellow to coppery-red and silver-gray (Koivula and Tannous, 2004a).

Within the Parana River basin, abundant large amethyst geodes occur in tholeiitic basalts and basaltic andesites of the 40-50 m thick Lower Cretaceous Serra Geral Formation in the Ametista do Sul region in the state of Rio Grande do Sul. The volcanics occupy an area of about 1 million km² and are as much as 800 m (2,500 feet) thick in some areas. Large portion of the basalts are mineralized over thicknesses of 2 to 10 m (6.4 to 32 feet). The amethyst, along with gray and colorless quartz, agate, celadonite, calcite and occasional barite, fills flat-lying joints in the amygdaloidal basalts and also cements local fracture zones. The locality in southern Brazil is well-known as a source of Palmeira amethyst (Schumann, 1997), including both faceting material and geodes. The color is lilac with a bluish tint and will turn brownish orange following heat treatment at temperatures of 435 to 475^oC (Kievlenko 2003).

Crystals occur within spherical to vertically elongated geodes up to 6 m in size, that are layered with an outer coating of celadonite [K(Mg,Fe²⁺)(Fe³⁺,Al)(Si₄O₁₀)(OH)₂ ] on top of agate. Inside the agate is found colorless quartz, which grades inward into amethyst. Calcite and gypsum may also be found within the geodes (Gilig and others, 2003). Using a variety of analysis techniques, including the study of fluid inclusions, Gilig and others (2003) hypothesized a two-stage process for the development of the geodes. First, fluid separation during magmatic cooling caused development of numerous cavities in the presence of lower density immiscible fluids within the basalt. This was followed by post-magmatic filling of the cavities at temperatures less than 100˚C by amethyst and other minerals. Crystallization of the geode-filling minerals was from a gas-poor circulating aqueous fluid that evolved from meteoric waters. This circulating fluid leached its mineral content from the highly-reactive interstitial glass indigenous to the basalt over a time that may have lasted for as much as 40 to 60 million years.

At the important Maraba deposit in the western portion of the State of Para, 270 miles south of Belem, fractures in Proterozoic quartzites are filled with light-violet amethyst aggregates (Schumann, 1997; Kievlenko 2003).

Canada Quartz-rich breccia zones along recurrent faults within an unconformity between Archean (2.7 Ga) and Proterozoic (2.0 Ga) rocks in the Thunder Bay – Lake Nipigon area of Canada are local exploration targets for amethyst. This 125 km long by 40 km wide amethyst region along the north shore of Lake Superior was the prehistoric source for amethyst used by native people. Modern mining there began in the 1860’s, but diminished in the early 1900’s with competition from material mined in Brazil. Renewed activity came in the 1950’s with the discovery of several large amethyst deposits.

Amethyst occurrences in the Thunder Bay amethyst region are related to the hydrothermal vein system responsible for the Dorion lead-zinc-barite veins and Thunder Bay silver. Vugs and zoned veins within this environment host amethyst ranging in color from almost black to very pale-violet. Market strength for as many as 14 producers, many of whom offer fee-digging, is rooted in spectacular amethyst specimens often found in combination with barite and fluorite, as well as in fine facetable material (Garland, 2004).

This amethyst field which includes the Thunder Bay, Diamond Willow, Dorion and Ontario gem mines lies along the northwestern coast of Lake Superior near Thunder Bay, Ontario. The amethyst is in barite-quartz veins that are up to 1.5 m (4.8 feet) thick. The veins occur in Late Archean granite gneiss, granite and quartz monzonite near the contact with Proterozoic sedimentary rocks. Veins, lenses and 15 to 25 m (48 to 80 feet) thick mineralized fractures are grouped in vein-stockwork zones that trend for 1.6 km (Thunder Bay) and 2.4 km (1-1.4 miles) (Diamond Willow). The amethyst was deposited on the walls of narrow fractures as radiating groups of fine crystals, compact aggregates, and large pyramidal shaped crystals up to 25 cm (10 in) in diameter that are found in clay-filled cavities in vein swells. These cavities may contain druse-like crystal aggregates in masses up to 300 kg.

The color of the amethyst ranges form pale lavender to dense violet. The amethyst is interpreted to have deposited in iron-rich solutions that were depleted in aluminum under oxidizing conditions at 90 to 250^oC and low pressures. The amethyst mineralizing event was preceded by quartz-barite-sulfide mineralization (Kievlenko 2003).

Chile Transparent rock crystal with phantoms formed by thin, platy, lead-gray metallic molybdenite inclusions have been recovered from the Confianza mine, Tilama, Valparaiso. These well-formed, singly- and doubly-terminated crystals are reported to have weights in excess of 10 kg (Koivula and Tannous, 2004d).

China Hydrocarbon inclusions within quartz are abundant in Sichuan Province, China (Hyrsl, 2004).

Europe Amethyst is mined in the Rhodope Mountains of Bulgaria (Balitsky, Balitsky, Bondarenko, and Balitskaya, 2004).

Iran Violet adularescent chalcedony has been mined from an area underlain by Eocene andesitic volcanic rocks near Qom Salt Lake in central Iran since 2003. The material is recovered as glauconite encased, irregular nodules that exhibit botryoidal structure and some agate-like color banding. The best adularescent chalcedony varies from dark-violet to light grayish-violet, and is accompanied by agate in colors of brown, orange, yellow, and pink. Production was reported in 2004 at 800 kg of chalcedony per month, with only about 150 kg exhibiting moderate tones of violet color. The translucent violet adularescent chalcedony, having a specific gravity of 2.59 and refractive index if 1.538, is processed into cabochons weighing up to 22.5 carats (Douman and Quinn, 2004).

Madagascar Colorless rock crystal quartz from the Sakavalana pegmatite, Fianarantsoa Province hosted a pink-zoned inclusion of pezzottaite (a Cs, Li-rich member of the beryl group) (Koivula and Tannous, 2005).

Chatoyancy resulting from coppery-red rutile within highly transparent quartz is one of many types of quartz that has come from Madagascar (Koivula and Tannous, 2004a).

Namibia Amethyst and citrine are produced from the Sarusas mine in a remote part of Skeleton Coast Park in the Namibia Desert of northwestern Namibia. Amethyst and rare pale citrine occur as geodes within basalt. Quartz mined here during the late 1960’s through the mid-1980’s was entirely shipped to Germany. The mine was reopened in late 2004, producing about 1500 kg of rough from which less than 1% was facetable. Cut stones weighed up 20 carats, with amethyst colored light to dark purple, and citrine an orange-yellow to deep orange. Commercial citrine is produced through heat treatment of amethyst at as much as 600˚C (Laurs, 2005b).

Pakistan Quartz crystals hosting both fluid and solid natural petroleum inclusions have been mined in Baluchistan (Koivula and Tannous, 2004b).

Russia Amethyst deposits are found in the Ural Mountains and Yakutia. One hundred kilometers north of Ekaterinburg in the Murzinka-Adui region of the Central Ural Mountains, a large amethyst deposit is found along on a contact between Late Paleozoic Murzinka granite with Cambrian biotite-amphibolite gneiss. Topaz- and beryl-bearing miarolitic pegmatites occur in gneiss, while hydrothermal amethyst is mainly in granite west of the Murzinka and Sizikova villages.

The principal amethyst deposit is the Vatikha in the Sizikovsky district. The district itself includes closely spaced quartz veins and mineralized fractures in granite. The quartz in the stockworks is associated with several faults that are mineralized along a 30 to 350 m (96 to 1120 feet) strike length. The veins range from 5 cm to 1 m (2 inch to 3.2 feet) thick and mineralization continues to depths of at least 150 m (480 feet) based on mining and drilling. The veins and stockworks are accompanied by intensely propylitized and argillized selvages that produce distinctly greenish altered granite. The walls of the fractures are coated with gray translucent quartz and the open veins contain some colorless and smoky quartz, amethyst and carbonates. The vein mineralogy also includes hematite, siderite, brookite, analcime along with secondary goethite, psilomelane and gypsum. Altered propylitized wall rock includes secondary kaolinite, sericite, chlorite, albite, carbonates, pyrite and quartz.

Another group of amethyst deposits are found 80 km (48 miles) southwest of Aldan in southern Yakutia. The amethyst is found in syenite porphyries at their contact with granites. Where found, the amethyst occurs in hydrothermally altered granite and syenite porphyries that contain numerous fractures and quartz lenses associated with sericitization, kaolinization, and silicification. The main amethyst zone occurs in a fracture zone in syenite that was traced for 165 m (528 feet) along strike. The amethyst is found in cavities in swells and at the intersections of veins and fractures. The cavities reach up to 3 m (9.8 feet) in length with cavity walls covered by druses of smoky quartz and crystals of amethyst that are 1 to 8 cm long (0.4 to 2.4 inches). These occur primarily unattached to the walls, lying in the clay-sand material filling the cavities (Kievlenko 2003).

Tajikistan The Selbur deposit in Tajikistan forms a large deposit of quartz with amethyst about 45 km (27 miles) west of Dushanbe in the Hissar Mountains. The deposit is part of a Middle-Upper Carboniferous volcano-sedimentary succession consisting of tuffaceous sandstones, siltstones, and limestones. The deposit consists of greenish-gray polymictic feldspar-quartz sandstones with sericite and chlorite that is cut by northerly trending fractures. These fractures zones exhibit silicification, potassic feldspathization, and locally some carbonatization and ferrugination, and contain numerous conjugate quartz-amethyst veins and lenses including a group of mineralized zones that are as much as 50 to 350 m (160 to 1120 feet) long and 1 to 8 m (3.2 to 25 feet) thick.

The veins and lenses are essentially quartz veins with some ankerite and calcite. The quartz is primarily milky with gray comb-like translucent quartz and amethyst in the central portions of the veins. Cavities are periodically found in the central portions of the veins, with radiating quartz and amethyst crystals – some of the larger cavities also contain orange-red clay. Amethyst crystals have prismatic habit and typically do not exceed 5 cm (2 inches) in length. These for the most part are cloudy and fractured, and not suitable for gems. The gem material occurs in the comb-like portions of the vein. The amethyst ranges from pale to intense violet with a smoky to reddish tint.

Near fracture zones, the sandstone is bleached and silicified and trapped xenoliths are intensively argillized. Other veins lacking in amethyst contain fine-grained sugary quartz and lack in alteration selvages (Kievlenko 2003).

United States

According to Kievlenko (2003) there are a number of small hydrothermal amethyst deposits in the US that are mainly found in the Appalachian Mountains in Virginia, North Carolina, South Carolina, and Maine. Other amethyst deposits are reported in Arizona and Montana.

Arizona High-quality deep purple amethyst is produced from crystal-filled or crystal-lined cavities in the Four Peaks mine near the south end of the Mazatzal Mountains in Maricopa County, about 75 km (46 miles) northeast of Phoenix. Smoky and transparent quartz are produced here as well. This deposit, considered by some to be the most important commercial gem-quality amethyst source in the United States, has been mined intermittently since the early 1900’s. Rough crystals may be as large as 20 cm (8 inches) in diameter, but most are only clear enough near their tips to supply gems (Sinkankas, 1959). Cut stones have exceeded 20 carats in size, and show a wide range of purple colors including a very dark-purple and reddish-purple. Uneven color zoning with banding parallel to rhombohedral crystal faces, crystal faces coated or frosted with hematite and apatite, and variable transparencies in rough crystals are characteristic of the deposit. Finished stones may host hematite flakes and fluid inclusions, and may show growth zoning and Brazil-law twinning, all of which distinguish amethyst from the Four Peaks mine from synthetic material. Heat treatment is used on 20-30% of Four Peaks amethyst to lighten its overly-dark color, although subsequent fracturing renders about 50% of the treated material useless (Lowell and Koivula, 2004).

Most recently, the mine on a 20-acre patented mining claim within the Four Peaks Wilderness Area and at an elevation of 1981 m (6500 ft), has been owned and operated by Four Peaks Mining Co., LLC out of Ocean Grove, New Jersey. The mine workings are limited to an open cut and a 10 m tunnel. Mining is accomplished using pneumatic and hand tools (Lowell and Koivula, 2004).

The Four Peaks represent Precambrian metasediments that were intruded by Proterozoic granite. Development of linear zones of brecciation within the light-colored Mazatzal quartzite accompanied granite emplacement. Irregular cavities, generally 0.3 to 1.2 m (1- to 4-ft) deep and up to 3 m (10 ft) long, within the brecciated quartzite host amethyst as well as rock crystal and smoky quartz. These crystals are thought to originate from silica-rich hydrothermal fluids derived from the cooling of the intrusive granite (Lowell and Koivula, 2004). Cavities are often clay-filled, with quartz crystals either attached to the walls or loose within the clay. Detached crystals commonly show signs of extensive corrosion, probably related to late stages of cavity development. Apatite and hematite are common accessory minerals, and minute fluorapatite and hematite crystals are found as coatings on corroded and etched quartz (Sinkankas, 1959).

Arkansas - Nearly flawless prismatic quartz is recovered from several deposits in Hot Springs County. The material exhibits excellent formed, transparent prisms terminated at one end by a pyramid.

California - Striking specimens of gold-in-quartz have been produced from the Badger mine, Mariposa County, California. The mine was first worked in the 1850’s, producing $80,000 in gold from shallow tunnels and trenches in the Prescott quartz vein system. The vein is up to 10 m wide, and is prominent throughout the mining area. Gold-in-quartz is also produced from the Sixteen-to-One mine in Sierra County (Laurs, 2005c).

Amethyst has been known for many years from the Kingston Range in San Bernardino County, California. Notable gem-quality material was recently extracted from the Purple Lily prospect, including crystals as much as 9 cm (3.5 in) in length. The amethyst occurs in cavities along northwest-trending fault zones and joints within granitic host rock. Amethyst crystals also are found within miarolitic cavities in areas of light-colored granite (Laurs, 2004).

Naturally occurring green quartz or prasiolite is found on the California-Nevada border (Quinn, 2004).

Colorado - Very large, well-formed translucent and smoky quartz crystals with some fluorite were found in the Holy Moses pocket on the Godsend claim located in the Crystal Creek area near Lake George south of Denver. The pegmatitic minerals were recovered from a miarolitic cavities in the Pikes Peak granitic batholith (1.02-1.08 Ga). The Pikes Peak granite forms the core of the Front Range of the Rocky Mountains in this region and includes numerous miarolitic pegmatites that have yielded exceptional specimens of smoky quartz, colorless quartz, topaz, microcline (including amazonite), goethite, albite and fluorite. The Lake George intrusive center of the Pikes Peak batholith is one of the more prolific sources for these pegmatites, and those found in the Crystal Creek area have been very productive in the past. The miarolitic cavities from this area typically are lense shaped – the largest being about 1.2 m (4 ft) high to 3 m (10 ft) long. However, recent exploration in this area led to the discovery of a series of cavities that have been excavated over a length of 13.5 to 15 m (45 to 50 ft) and widths of 1.8 to 3.2 m (6 to 10 ft). Crystals recovered from this cavity included a doubly-terminated smoky quartz crystal of 1.3 m (4.2 ft) in length weighing 235 lbs, another 1.2 m (4 ft) specimen weighing 439 pounds with translucent blue fluorite specimens up to 15 cm (6 inches) across (Berry and Fretterd 2003).

Georgia - Amethyst crystals have been surface mined since the mid-1980’s from weathered granitic host rock near Jackson’s Crossroads in Wilks County, Georgia, about 150 km (93 miles) east of Atlanta. Recent mining, beginning in 2004, by Terry Ledford and Rodney Moore has produced cut stones larger than 48 carats that display a deep purple color in incandescent light and a noticeably more blue color in daylight. The site is open to public fee-digging (Laurs, 2005a).

Montana - Amethyst is found in the Toll Mountain pegmatite in the southwest portion of Jefferson County near Butte. The miarolitic pegmatites are found in Mesozoic granite of the Boulder Batholith and are concentrated near granodiorite and quartz monzonite facies in the batholith. The principal deposits, referred to as the Pohndorf and Little Gem mines, were developed on three stock-like pegmatites. Amethyst is also reported in the East Range, Timber Butte, Lake Delmo and Goldflint Mountain areas (Kievlenko 2003).

New York - Doubly-terminated quartz crystals from Herkimer County, New York have been known to host amorphous hydrocarbons as inclusions, referred to as “asphaltite” or “anthraxolite”. These originate within silicified dolomites, and appear to have developed during digenesis of the host rock (Hyrsl, 2004). Hydrocarbon inclusions are also known from other localities around the World, however, those from Herkimer are the best known. The small colorless quartz crystals from this deposit are widely known as ‘Herkimer diamonds’ (Hurlbut and Switzer, 1979).

North Carolina - Coppery-red rutilated quartz has been mined from North Carolina (Koivula and Tannous, 2004a).

Wyoming - Many varieties of quartz and chalcedony have been found in Wyoming. Good specimens of prismatic quartz are uncommon in Wyoming, but the state has yielded many attractive specimens of chalcedony. Much of the crystalline quartz found in the state has been cloudy and translucent to opaque. However, specimens of chalcedony are quite varied, and Wyoming has become a favorite collecting ground for agate, jasper, flint, and petrified wood.

Many different agates are found near Guernsey in the Hartville uplift of eastern Wyoming. These have attracted rock hounds and mineral collectors for years, and many varieties of agate have received local names. For example, one local agate known as Youngite, forms distinct rehealed limestone breccias consisting of pink- to cream-colored breccia clasts of Guernsey Limestone that are cemented by light-grey to greyish blue, banded, drusy quartz and chalcedony (Figure 3.43). The drusy quartz fills fractures in the breccia and completely encases the brecciated limestone clasts. When polished, the contrasting colors of the quartz and breccia clasts provide very attractive lapidary stones. Under long wavelength fluorescent light, these samples yield a blue network of fluorescence that follows the bands of drusy quartz. Samples of Youngite are of relatively high-value.

Another popular agate found in the same region is the Slater agate. Slater agates form concretionary masses with white coatings. When cut, the interior of the stones are typically dark grey to black agate surrounding milky, agatized, interiors with small, fine, agatized dendrites. The surface of some of these agates is porous and may give an impression of a fossilized sponge.

Petrified wood, quartz, and chalcedony are found in the Laramie, Sierra Madre and Seminoe Mountains, and in the Shirley, Laramie, Goshen Hole, and Saratoga Valleys in southeastern Wyoming. The most common forms of chalcedony in this region are agates and jaspers eroded from Paleozoic limestones, particularly, the Casper Formation. Some petrified woods from this region are probably derived from silica leached from Tertiary volcanic ash falls, that later replaced the wood.

In the Saratoga Valley, agatized and opalized woods and dendritic agates are found on the flats north of town. The host rock was possibly tuffaceous sandstone, siltstone, and claystone of the North Park Formation.

Beautiful specimens of jasperized iron formation are found in the Seminoe Mountains several miles northwest of Saratoga, and north of Sinclair. These rocks are magnetic and have alternating bands of black magnetite, dark gray quartz, and tawny to brown layers of jasper and grunerite. The source of this material is banded iron formation from Bradley Peak in the Seminoe Mountains gold district. Much of the jasperized material is found as cobbles and pebbles downstream along Deeweese Creek and in alluvium along the north flank of the range near the Miracle Mile on the North Platte River. This area should also be of interest to the gold prospector. The Miracle Mile is surrounded by a dry placer formed of unconsolidated gravels located several feet above the river banks. The authors have recovered gold colors from badger and other burrowing animal diggings in this region. They have also found diamond stability pyrope garnets associated with pediment gravels in the same area.

At Shirley Basin east of the Seminoe Mountains, several agates and jaspers have originated from Casper Formation limestones and sandstones. One agate is a reddish-brown jasper mixed with dark gray to black opaque agatized breccia near Mine Hills and Crystal Hill to the south of Marshall. This rock consists of pink breccia clasts of Casper Formation sandstone cemented with reddish-brown and massive black chert coated with tiny grains of psilomelane (metallic, manganese oxide) that produces an attractive decorative stone. Along the southern end of the basin, the Shirley uplift is famous for silicified dinosaur bones found on both sides of Como Bluff north of US Highway 287/30 near Medicine Bow (Sinkankas, 1959).

Near Battle Lake in the Sierra Madre Mountains southwest of Saratoga, quartz crystals occur in cavities and fractures in red granite. The quartz includes amethyst, rose, smoky, milky white, and clear quartz crystals. Most are small and less than 2 inches in length. This region is also known for its old copper mines and several significant gold, platinum, palladium, nickel, and zinc anomalies.

The Absaroka Mountains in northwestern Wyoming, have produced a variety of petrified woods and agates. Along the western margin of the range, Yellowstone Park is famous for its fossil forests at Specimen Ridge and Amethyst Mountain. Some prostrate fossilized trunks have been found in this region that are more than 50 feet long, and 5 feet in diameter (Sinkankas, 1959). Amethyst is also reported in the Yellowstone area at Amethyst Mountain (keep in mind, collecting is prohibited in the National Park).

Wood casts, fossil cone casts, agatized seeds, and oval nodules have also been found in this region. These are clear, gray, brown, yellow, green, and red with patterns that include fortifications, banding, spots, moss, tea leaf, and iris agate. Wiggins Fork agates, petrified wood, and Montana agates are also found along the Yellowstone River as far east as Glendive, Montana.

East of the Absaroka Mountains, chert, agate, and jasper occur in Paleozoic limestones along the eastern flank of the Bighorn Basin, along the southern margin of the Bighorn Mountains, and the north side of the Owl Creek Mountains. Woodcast agates are reported along the Bighorn River and in several drainages on the western margin of the basin. Green agates and crystal-lined geodes have also been reported along Cottonwood Creek near Hamilton Dome.

A colorful red and white banded fortification agate, known as the Dryhead, weathers out of the Phosphoria Formation in the northern Bighorn Basin. This agate is named for the barren Dryhead country, which form the cliffs along the Bighorn River north of the Wyoming-Montana state line. In the Wind River Basin to the south of the Owl Creek Mountains, rainbow agates are found along the Wind River near Riverton.

In the Black Hills of northeastern Wyoming, some chalcedony and amethyst is found. Agates and jasperoids are also reported in stream gravels along with gold colors and nuggets in the Mineral Hill district of the Black Buttes east of Sundance. These appear to be related to Tertiary alkalic volcanic rocks.

In the Powder River Basin, west and south of the Black Hills, several varieties of petrified wood, chert and jasper are found. The chert and jasper are associated with Paleozoic limestones along the western margin of the basin, and the petrified wood is derived from the Wasatch Formation. Occasionally, some spectacular, large-diameter stumps and logs are found. East of Buffalo at the Dry Creek Petrified Tree site, poorly silicified, brittle, wood is found that easily crumbles into small pieces. The petrified wood in this area is primarily of scientific interest and is not suitable for polishing.

Another petrified wood, the Crazy Woman Creek wood, is more durable and suited for lapidary. This wood is silicified, banded in shades of brown and white, and found in terrace gravels about 60 to 120 feet above Crazy Woman Creek in an area extending from the Bighorn Mountains to where Dry Creek joins Crazy Woman Creek. Large pieces (longer than 1 foot in length) of the Crazy Woman petrified wood were found in the vicinity of Crazy Woman Creek in the past, and can still be found in landscaping and local collections in Buffalo. Similar material has been found in terrace gravels along the Powder River near Kaycee. East of Buffalo, amethyst-lined cavities were reported in some specimens of petrified wood.

The Granite Mountains in central Wyoming are known for jade. In addition, several types of agate, jasper, and petrified wood and some rubies and sapphires have been found. One of the better-known varieties of agate is the Sweetwater moss agate which usually occurs as small pebbles in lag gravel and in the basal conglomeratic sandstone of the Split Rock Formation. These agates fluoresce brilliant yellow due to the presence of hydrous uranium arsenate. They often contain a brown, opaque surface that can be removed by tumbling. Tumbling results in a highly polished, light gray to blue agate with black manganese dendrites.

In the same general region, the Ice Point Conglomerate, has rounded fragments of black petrified wood, and the Bridger Formation contains fossil tree stumps, fragments of petrified wood, and dark gray and brown agates (Love, 1970). Some clear chalcedony balls have also been found, that are coated with opal and white ash. These have loosely been termed 'moonstones'. Another popular agate, the 'Angel' agate, is found in a 6 inch zone in the upper porous sandstone of the Split Rock Formation. The agate occurs in nodules and is an attractive pale-greenish-gray color with a chalky-white surface coating. The agates fluoresce a brilliant greenish-yellow under ultraviolet light, and are slightly radioactive (Love, 1970).

In the nearby Tin Cup district, beautiful jasperized breccias with angular fragments of blood-red, chocolate-brown, and butterscotch yellow-brown jasper occur along three prominent faults which were prospected for gold in past years. Some attractive chalcedony in this area is gray, banded, folded agate.

In the Eden Valley in southwestern Wyoming, petrified wood is found over a wide area around Farson. This wood resembles ordinary weathered wood and has an opaque cream colored coating of silica covering a silicified black to brown core. The Laney Shale Member of the Green River Formation and the overlying Bridger Formation appear to be the source of this material.

Locally the Bridger Formation contains petrified wood near Oregon Buttes. This wood, known as the Bridger-type, consists of partially silicified black wood. Where it is completely replaced by silica, it ranges in color from brown, tan to green. Some clear chalcedony and vein moss agates are found nearby, as well as paleoplacer gold.

Some of the more striking wood found in Wyoming is Blue Forest agate west of Farson in the Eden Valley. The wood has a black to brown central core surrounded by clear blue chalcedony which producing an unique and very attractive, silicified wood.

Reefs and beds of silicified gastropods (fossil snails), which were deposited in a prehistoric lake, are found throughout the area. Some of the better collecting localities occur along Delany Rim south of Interstate 80 near Red Desert west of Rawlins, and to the west of Rock Springs. Some fossil snails are light-brown in color and have a weathered appearance, and will not polish. The darker agates found in shades of dark brown to black, will generally polish, and produce attractive bookends.

Banded jasperoids on Quaking Asp Mountain south of Rock Springs consist of dark- to light-gray banded agate with cross-cutting veins of quartz, and banded red, yellow-orange, and gray jasperoid and onyx. These occur in a very large and extensive silicified zone associated with ancient hot

springs. Some of these will produce beautiful lapidary stones (Hausel and Sutherland, 1998).

Uruguay Uruguay produces amethyst and other quartz gems, including agate, from deposits similar to those found in its neighbor, Brazil.

Zambia Hydrothermal amethyst mineralization in Zambia is related to boundary faults that separate basement Mesoproterozoic gneisses and metasediments that are intruded by Late Proterozoic granitoids from Mississippian-Late Triassic Karoo rocks. Amethyst deposits are contained in veins and stockworks along these faults that occur within the basement complex at many places in Zambia. The most important production comes from the Southern Province in the Mwakambiko Hills and in the Mumbwa-Namwala area, adjacent to Lake Kariba near the boundary with Zimbabwe (Kievlenko, 2003). Amethyst production from Zambia amounts to about 700 tonnes per year, with the largest amount coming from Mwakambiko. The Mwakambiko deposit is hosted in granosyenite that has intruded hornblende gneiss, quartzites, and marbles. Abundant quartz-amethyst veins and lenses up to 1 m (3.3 feet) thick cut the brecciated, silicified, and hematite-enriched host rock in a northerly trend for 3.5 km (2.2 mi). Amethyst from the Mwakambiko deposit is extracted primarily from eluvial debris Kievlenko (2003).

References
Hausel, W.D., and Sutherland, W.M., 2006, World Gemstones: Geology, Mineralogy, Gemology & Exploration: WSGS Mineral Rept MR06-1, 363 p.

Agate, Jasper, Quartz, Chalcendony in Wyoming

2011-04-19T11:19:00.000-07:00

Youngite cab from the Hartville area

QUARTZ (CHALCEDONY)

Many varieties of quartz and chalcedony have been found in Wyoming. Good specimens of prismatic quartz are uncommon in Wyoming, but the state has yielded many attractive specimens of chalcedony. Much of the crystalline quartz found in the state has been cloudy and tranlucent to opaque. However, specimens of chalcedony are quite varied, and Wyoming has become the favorite collecting ground for collectors of agate, jasper, flint, and petrified wood. (I would like to acknowledge my old field partner, Wayne Sutherland, who provided me with considerable library research on this subject when I was at the Wyoming Geological Survey).

These include agates near Guernsey in the Hartville uplift of eastern Wyoming. Many agates in this area, have attracted rock hounds and mineral collectors for years, and many varieties of agate have received local names. For example, one local agate known as Youngite, forms distinct rehealed limestone breccias consisting of pink- to cream-colored breccia clasts of Guernsey Limestone that are rehealed and cemented by light-grey to greyish blue, banded, drusy quartz and chalcedony. The drusy quartz fills fractures in the breccia and completely encases the brecciated limestone clasts. When polished, the contrasting colors of the quartz and breccia clasts provide very attractive lapidary stones. Under long wavelength fluorescent light, these samples yield a blue network of fluorescence that follows the bands of drusy quartz. Samples of Youngite are relatively high-value.

Petrified wood, quartz, and chalcedony are found in the Laramie, Sierra Madre and Seminoe Mountains, and in the Shirley, Laramie, Goshen Hole, and Saratoga Valleys in southeastern Wyoming. The most common forms of chalcedony in this region are agates and jaspers eroded from Paleozoic limestones, particularly, the Casper Formation. Some petrified woods from this region are probably derived from silica leached from Tertiary volcanic ash falls, that later replaced the wood.

In the Saratoga Valley, agatized and opalized woods and dendritic agates are found on the flats north of town. The host rock was possibly tuffaceous sandstone, siltstone, and claystone of the North Park Formation.

Banded iron formation, Seminoe Mountains. From the Tom Nissen
collection, Laramie, Wyoming.

Beautiful specimens of jasperized iron formation are found in the Seminoe Mountains several miles northwest of Saratoga, and north of Sinclair. These rocks are magnetic and have alternating bands of black magnetite, dark gray quartz, and tawny to brown layers of jasper and grunerite. The source of this material is banded iron formation from Bradley Peak in the Seminoe Mountains gold district, and much of the jasperized material is found as cobbles and pebbles downstream along Deeweese Creek and in alluvium along the north flank of the range near the Miracle Mile on the North Platte River. This area should also be of interest to the gold prospector. The Miracle Mile is surrounded by a dry placer formed of unconsolidated gravels located several feet above the river banks. The author has recovered gold colors from badger and other burrowing animal diggings in this region.

At Shirley Basin east of the Seminoe Mountains, several agates and jaspers have originated from Casper Formation limestones and sandstones. One agate is a reddish-brown jasper mixed with dark gray to black opaque agatized breccia near Mine Hills and Crystal Hill to the south of Marshall. This rock consists of pink breccia clasts of Casper Formation sandstone cemented with reddish-brown and massive black chert coated with tiny grains of psilomelane (metallic, manganese oxide) that produces an attractive decorative stone. Along the southern end of the basin, the Shirley uplift is famous for silicified dinosaur bones found on both sides of Como Bluff north of US Highway 287/30 near Medicine Bow (Sinkankas, 1959).

The Absaroka Mountains in northwestern Wyoming, have produced a variety of petrified woods and agates. Along the western margin of the range, Yellowstone Park is famous for its fossil forests at Specimen Ridge and Amethyst Mountain. Some prostrate fossilized trunks have been found in this region that are more than 50 feet long, and 5 feet in diameter (Sinkankas, 1959). Amethyst is also reported in the Yellowstone area at Amethyst Mountain (keep in mind, collecting is prohibited in the National Park).

In the Black Hills of northeastern Wyoming, some chalcedony and amethyst is found. Agates and jasperoids are also reported in stream gravels along with gold colors and nuggets in the Mineral Hill

district of the Black Buttes east of Sundance. These appear to be related

to Tertiary alkalic volcanic rocks.

Sweetwater moss agate, Wyoming

The Granite Mountains in central Wyoming are known for jade. In addition, several types of agate, jasper, and petrified wood and some rubies and sapphires have been found. One of the better known varieties of agate is the Sweetwater moss agate which usually occurs as small pebbles in lag gravel and in the basal conglomeratic sandstone of the Split Rock Formation. These agates fluoresce brilliant yellow due to the presence of hydrous uranium arsenate. They often contain a brown, opaque surface that can be removed by tumbling. Tumbling results in a highly polished, light gray to blue agate with black manganese dendrites.

In the same general region, the Ice Point Conglomerate, has rounded

fragments of black petrified wood, and the Bridger Formation contains fossil tree stumps, fragments of petrified wood, and dark gray and brown agates (Love, 1970). Some clear chalcedony balls have also been found, that are coated with opal and white ash. These have loosely been termed

'moonstones'. Another popular agate, the 'Angel' agate, is found in a 6 inch zone in the upper porous sandstone of the Split Rock Formation. The agate occurs in nodules and is an attractive pale-greenish-gray color with a chalky-white surface coating. The agates fluoresce a brilliant greenish-yellow under ultraviolet light, and are slightly radioactive (Love, 1970).

In the Eden Valley in southwestern Wyoming, petrified

wood is found over a wide area around Farson. This wood resembles ordinary weathered wood and has an opaque cream colored coating of silica covering a silicified black to brown core. The Laney Shale Member of the Green River Formation and the overlying Bridger Formation appear to be the source of this material.

Reefs and beds of silicified gastropods (fossil snails), which were

deposited in a prehistoric lake, are found throughout the area. Some of the better collecting localities occur along Delany Rim south of Interstate 80 near Red Desert west of Rawlins, and to the west of Rock Springs. Some fossil snails are light-brown in color and have a weathered appearance, and will not polish. The darker agates found in shades of dark brown to black, will generally polish, and produce attractive bookends.

springs. Some of these will produce beautiful lapidary stones (Hausel and Sutherland, 1998).

Absaroka Mountains and Vicinity. Volcanic rocks of the Absaroka Volcanic Supergroup (Eocene) within the Absaroka Mountains, contain scattered fragments of petrified wood and agate. Along the western margin of the Absaroka Mountains, Yellowstone Park is famous for its fossil forests, particularly at Specimen Ridge and Amethyst Mountain. Some prostrate fossilized trunks have been found in this region that are more than 50 feet long, and 5 feet in diameter (Sinkankas, 1959). Some amethyst has also been reported at Amethyst Mountain, but the collected should remember that collecting is not permitted within the National Park.

Petrified wood in the form of silicified logs, trunks, and stumps is found in many areas in northwestern Wyoming, and includes upright pieces that resemble burned-out forests. Wood casts, fossil cone casts, agatized seeds, and oval nodules are also found. These materials range in color from clear to grey to brown, yellow, green, and red with patterns that include fortifications, banding, spots, moss, tea leaf, and iris agate. Some oval nodules in this region may be remnants of chalcedony-filled visicles in lava or scoria beds (Keenan, 1964). In addition, Wiggins Fork agates and petrified wood, and the Montana agates, are found along the Yellowstone River as far east as Glendive, Montana (Sutherland, 1990).

T45N, R106W (recommended map - US Geological Survey, Ramshorn 1:100,000 topographic quadrangle). Wiggins Fork petrified wood and agate are fairly abundant in the Wiggins Formation along the Wiggins Fork River and Frontier Creek. Large areas in this region are closed to collecting, and collectors should contact the Shoshone National Forest office to obtain information on which areas may be open to collecting.

T43-44N, R107-108W (recommended map - US Geological Survey, Ramshorn 1:100,000 topographic quadrangle). Horse Creek, Burrows Creek, and many other streams in this area have been reported as good collecting localities for petrified wood and agate (Cheyenne Mineral and Gem Society, 1965). The wood and agate are derived from the Wiggins Formation. Some material is found in terrace and stream gravels in this region. Volcanic material other than the Wiggins Formation may also contribute to the petrified wood and agates in this area. Some chalcedony may also be derived from Paleozoic limestones (Sutherland, 1990).

T54N, R104W (recommended map, US Geological Survey, Cody 1:100,000 topographic quadrangle). Jasperoid is reported in Paleozoic sedimentary rocks in the western part of this township (Nelson and others, 1980; Hausel, 1989).

Bighorn Basin-Owl Creek Mountains. Chert, agate, and jasper occur in Paleozoic limestone along the eastern flank of the Bighorn Basin, the north side of the Owl Creek Mountains, and in gravels in various drainages in this region. Woodcast agates are reported along the Bighorn River and several drainages on the western flank of the basin. Johnson (1973) also reported green agate and crystal-lined geodes were found along Cottonwood Creek near Hamilton Dome. Petrified wood is also reported a few miles north of Shell (Sutherland, 1990).

Nodular fortification agates occur along outcrops of the Phosphoria Formation along the southern and eastern flanks of the Pryor Mountains. The agates are most abundant just north of the state line in Montana near the confluence of Dryhead Creek and the Bighorn River (Cheyenne Gem and Mineral Society, 1965).

Dryhead agate (T58N, R94-95W). A colorful red and white banded forification-type agate, known as the Dryhead agate, weathers out of the Phosphoria Formation in the northern Bighorn Basin. Some bands in this material will fluoresce green under short wavelength ultraviolet light (Breitweiser, 1966). This agate is named for the barren Dryhead country headlands, which form the cliffs along the Bighorn River just north of the Wyoming-Montana state line (Sutherland, 1990) (recommended map - US Geological Survey, Powell 1:100,000 topographic quadrangle).

Spanish Point (sections 20, 21, 28, 29, 32 & 33, T52N, R88W) (recommended map - US Geological Survey, Worland 1:100,000 topographic quadrangle). Moss agate, chalcedony, and chert are found in Paleozoic limestones near Spanish Point (Sutherland, 1990). Root (1977), described this agate as a brown- to cream-colored moss agate.

Trapper Canyon (NE SW section 24, T52N, R89W). Dendritic agates were found on the Jack No. 1 mining claim in the Trapper Canyon area on the Trapper Galloway Ranch near Shell, Wyoming (letter from Kit Smith, July 12, 1988) (recommended map - US Geological Survey, Worland 1:100,000 topographic quadrangle).

T45-46N, R94-95W (recommended map - US Geological Survey, Thermopolis 1:100,000 topographic quadrangle). Limb cast agates are found along the Bighorn River (Keenan, 1964; Johnson, 1973). These agates are grey to white and are similar to the Wiggins Fork wood found many miles west in the Absaroka Mountains (Sutherland, 1990).

Black Hills. The Black Hills in northeastern Wyoming, contains minor amounts of chalcedony and uncommon amethyst. In the Mineral Hill district east of Sundance, agates and jasperoids have been found in stream gravels (Hausel, 1986). Many of these appear to be related to Tertiary alkalic volcanic rocks in the area. Further south, some poor quality petrified wood has been reported southwest of Newcastle (Sutherland, 1990). (recommended map - US Geological Survey, Sundance 1:100,000 topographic quadrangle).

Black Buttes(section 26, T50N, R62W). A narrow zone of silicification in the Pahasapa Limestone (Mississippian) lies a few feet above a trachyte porphyry sill (Tertiary). Within this altered zone, a narrow, reddish-brown to dark grey jasperoid with narrow veins of white quartz and vugs lined with quartz and white hemimorphite are found (Elwood, 1979). Locally, samples contain bright waxy, yellow-orange specs of wulfenite, massive galena in limestone breccia with some minor fluorite (Hausel, 1988c) (see also Ore Minerals).

Mineral Hill district. Located along the South Dakota-Wyoming border northeast of Newcastle and southeast of Sundance. Veins and pods of jasper and jasperoid are found in the Deadwood Formation (Cambrian) in an semicircular outcrop around Mineral Hill (Welch, 1974). The Deadwood Formation consists of carbonate-rich siltstones, sandstones, and flat-pebble conglomerate. Access to the Mineral Hill area is by Forest Service road. The district is heavily vegetated and many rock outcrops are hidden in the brush.

Artic #2 Mine (section 32, T51N, R60W). Purple chalcedony with small amethyst crystals on drusy quartz was discovered in a pyroxenite at the Artic #2 mine at the base of Mineral Hill (Figure 68) (Hausel, personal field notes, 1988). The amethyst appears to be rare, but its presence suggest other sources may occur in the district.

Granite Mountains, central Wyoming. The metamorphic rocks in the Tin Cup, Rattlesnake Hills, and Barlow Gap areas are excellent places to search for chalcedony in the Granite Mountains. In addition, many of the Tertiary sedimentary rocks scattered throughout the region also contain detrital fragments of chalcedony. Agates, jasper, petrified wood, gold, uranium, jade, iron, minor copper, spodumene, apatite, tourmaline, and corundum have all been found in the Granite Mountains.

One of the better known varieties of chalcedony, known as the Sweetwater moss agate, has been collected from this region for decades. The Sweetwater moss agates occur as small pebbles in lag gravel and is also found in the basal conglomeratic sandstone of the Split Rock Formation.

Another unit, known as the Ice Point Conglomerate, contains rounded fragments of black petrified wood. The Bridger Formation in the same region, is a source of fossil tree stumps, water worn fragments of petrified wood, and dark grey and brown agates. Agates have also been found in the Moonstone and Bug Formations in this region (Love, 1970).

Clear chalcedony balls found in the region, are sometimes coated with opal and white ash. These have been loosely termed ‘moonstones’ (Cheyenne Gem and Mineral Society, 1965). Love (1970) produced an excellent treatise on the Granite Mountains and its mineral and rock resources. It is highly recommended that the collector obtain a copy of this publication, as it will greatly assist in finding collecting sites in the region (recommended maps - US Geological Survey, Lander, Rattlesnake Hills, and Baroil 1:100,000 topographic quadrangles).

Agate Flats (T30-31N, R90W). Located between Sage Hen Creek and Diamond Springs Draw. This area has been intensely prospected during the past century for Sweetwater moss agates. Some agates may still be found in outcrop or in the adjacent pediments derived from the Split Rock Formation in an area covering about 50 mi² (Love, 1970). These agates have also been reported in gravels many miles down stream (Sutherland, 1990).

Agate Lake. Very fine moss agates are reported north of the Sweetwater River in the vicinity of Agate Lake (Cheyenne Gem and Mineral Society, 1965).

Barlow Gap (SW section 9, T31N, R88W). The Barlow Gap area lies south of the Rattlesnake Hills. This area is a great place to look for a variety of chalcedony as it is relatively secluded, and much of the area is located on public land. In addition to chalcedony, the rock hound and mineral collector may enjoy searching for old 50 caliber shells, as the Barlow Gap and Rattlesnake Hills areas apparently were part of a target range for World War II fighters. The history of the area also extends to early Indian activity, as teepee rings can still be found in the Barlow Springs area (Wayne Sutherland, personal field notes, 1998).

The Barlow Gap region is underlain by Tertiary sedimentary rocks, some Tertiary alkalic volcanic rocks, and by very old Archean metamorphic rocks. The metamorphic rocks include quartzites, amphibolites, granite gneisses, mica schists, and some banded iron formation. The iron formation is a source of common jaspers and some agates. Thus it is recommended that the collector obtain a geological map of the area and search the regions underlain by iron formation. In particular, an abundance and variety of jaspers and agates are found associated with iron formation in the SW section 9. These include brown, tawny, black, red, milky, and bluish-grey agates and jaspers (Hausel, personal field notes, 1998).

Crooks Gap (sections 29, 30, 31 & 32, T28N, R92W). Johnson (1973) reported agates from the Crooks Gap area south of Jeffrey City.

Dry Creek (SW SE section 5, T30N, R87W). A 10-foot-thick conglomeratic layer at the top of the Pliocene-Pleistocene Bug Formation in the vicinity of Dry Creek, contains dark-grey and amber agates (Love, 1970). Some of these agates fluoresce yellow under ultraviolet light (Sutherland, 1990).

Rawlins Draw Angel agates (SW NW section 36, T29N, R89W). (Recommended map - US Geological Survey, Baroil 1:100,000 topographic quadrangle). A zone of chalcedony nodules, known as "angel agates", are found in a 6-inch-thick zone in the upper porous sandstone of the Split Rock Formation (Tertiary). The mineralized zone is about 5 feet below a 10-foot-thick pumicite marker bed in the Rawlins Draw area, north of Muddy Gap near the Rawlins Draw drainage. These nodules have an attractive pale-greenish-gray color and are typically 1 to 3 inches in diameter with a chalky-white surface coating. The agates fluorese a brilliant greenish-yellow under ultraviolet light, and are slightly radioactive (Love, 1970). The agates have been quarried for lapidary use in the past (Sutherland, 1990).

Sweeny Basin (T29-30N, R95W). Moss agates are found both upstream and downstream from Highway 287, where the highway crosses the Sweetwater River in the vicinity of Sweetwater Station (Johnson, 1973; B. Dunbar, personal communication to Sutherland, 1990).

Sweetwater moss agate (NE section 16, T31N, R91W). Sweetwater moss agates are reported in the lower porus sandstone of the Split Rock Formation along the northern flank of the Granite Mountains. The agate occurs as 1 to 4 inch diameter nodules in the sandstone. The agates are radioacitive and will fluoresce a brilliant yellow due to the presence of trögerite, an hydrous uranium arsenate. The agates often contain a brown, opaque surface that can be removed by tumbling. Tumbling results in a polished, light grey to blue agate with black manganese dendrites (Figure 69) (Love, 1970).

White Ridge Agate Beds (Section 14, T30N, R90W): Agate pebble reefs and bedded chalcedony are found in the lower 500 feet of the Moonstone Formation (Pliocene). These extend east into the next two townships. The agates are rounded, and vary from 0.25 to 0.5 inch in diameter, and crop out in low ledges over a distance of about 1 mile. The agates vary from translucent brown to grey and a few have moss-like inclusions (Love, 1970). Fossil wood is also found nearby in the Moonstone Formation (Sutherland, 1990).

Wyoming ‘diamonds’ (T31N, R90W). Within the area around Diamond Springs Draw, small, clear, quartz crystals were at one time relatively common in the Sweetwater agate beds. These have been referred to as ‘Wyoming diamonds’, because of their clarity, small size, and symmetrical shape (Sutherland, 1990). However, they are quartz rather than diamonds.

Rattlesnake Hills, The Rattlesnake Hills district lies along the northern margin of the Granite Mountains. This terrane consists of an Archean greenstone belt fragment intruded by Tertiary alkalic igneous rocks. The area has high-potential for the discovery of large-tonnage commerical gold deposits, and contains several jasperoids and breccias in vein-like deposits known as exhalites (Hausel, 1996e). Agates are also found in the pediment gravels along the southern margin of the district (Figure 70).

Lost Muffler (SW section 16, SE section 17, NE section 21, and NW section 22, T32N, R87W). The Lost Muffler mineralized zone was mapped by Hausel (1996e) along UT Creek in the Rattlesnake Hills (Figure 51). This mineralized zone consists of a cherty unit associated with jasperoid, quartz, graphitic schist, and local pyrite, minor galena and arsenopyrite.

Jasper Knobs (W/2 NW section 35, T32N, R88W). Two hills on either side of the Dry Creek Road occur along a north-south trend and are located along the southern edge of the Rattlesnake Hills. These two hills are covered with banded golden brown and red jasper in limestone (Hank Hudspeth, Jr., personal communication to Sutherland, 1989). The jasper is massive, and covers an area of about 10 acres. The outcrop forming the hill on the north side of the Dry Creek road is a deep, blood-red, and is easily spotted from the road (see: Barlow Gap 1:24,000 and Rattlesnake Hills 1:100,000 scale topographic maps for access routes). The deposit is interbedded in a limy rock, and may represent a paleo-hot spring.

Several other jasper and agate deposits are found in the Barlow Gap-Rattlesnake Hills area, but are much smaller than the Jasper Knobs. These include red and brown jasper along a shear zone in the SE NW section 34, T32N, R88W, a small pod of red and brown jasper in Precambrian host rock on the south side of a breccia zone in the NE SW section 26, T32N, R88W. In addition, pale yellow, gray, and white layered agates in rough slabs up to 4 inches thick and 10 inches long are found along the east side of a ridge in the NE SE section 15, T32N, R88W.

Tin Cup District, The Tin Cup district in the western Granite Mountains is underlain by amphibolite-grade metamorphosed Archean gneiss, schist, and amphibolite intruded by granite. The northern portion of the district includes three prominent faults that have a total strike length of nearly 7 miles and have scattered outcrops of jasper (Figure 25). A few mines were developed along the southernmost fault in the search of gold in the 1800s, these include the Red Boy and Sutherland mines. Apparenly no gold was found, but some massive sulfide (pyrite) was intersected.

Recent investigations by Hausel (1996c,d) identified ruby, sapphire, jade, and jasper in the district (recommended map - US Geological Survey, Rattlesnake Hills 1:100,000 topographic quadrangle).

Sutherland-Red Boy mines (sections 25 & 36, T31N, R93W). The Sutherland shaft was sunk in a gossan and intersected massive pyrite at a shallow depth. Samples of massive pyrite and banded gneiss with stratiform pyrite can be found on the mine dump. In addition, beautiful specimens of jasperized breccia are found in a mine adit driven on the same structure a short distance northeast of the shaft. The breccia contains angular fragments of blood-red, chocolate-brown, and butterscotch-yellow-brown jasper with minor agate in a granular matrix.

Approximately 1,000 feet to the southwest along the same structure, quartz-rich schist and jasper were found on a dump and was mined from a adit estimated to be about 50 feet in length (Hausel, personal field notes, 1995). Further southwest, about 2,500 feet from the Sutherland shaft, some copper-stained jasper with minor malachite, azurite, and tenorite with a trace of chalcocite was found (Hausel 1996c).

Tin Cup Mountain (sections 24 & 27, T31N, R93W, and section 19, T31N, R92W). North of the Red Boy-Sutherland structure, jasperoids are found in two parallel faults. Beautiful red jaspers with jasperoid breccias and grey, banded, isoclinally folded agates were found along these two structures which are 3 to 4 miles in length. Common, massive, jasper with jasperoid breccia, was also found in the W/2 section 27, T31N, R93W. Other beautiful specimens of red jasper and grey and white banded jasperoid (agate) were found in several of the prospects along the three faults.

The agates and jaspers from this area produce exquisite pieces of polished rock. In particular, beautiful specimens of folded agate and red to butterscotch jasper were collected from prospects in section 24, T31N, R93W and in section 19, T31N, R92W (Hausel 1996c).

S/2 S/2 SE section 25, T31N, R93W. A prospect pit located along trend between the Sutherland and Red Boy mines contains dump material with quartz, opalized quartz, and jasperoidal hematite. The jasper is also found in place between sheared amphibolite and hematitic schist (Hausel, personal field notes, 1995).

W/2 NW section 25, T31N, R93W. A shallow shaft surrounded by a fence, contains minor quartz and jasper on the mine dump. This prospect lies on a parallel fault near the north end of the Red Boy-Sutherland structure (Hausel, personal field notes, 1995).

Beaver Rim Agates are reported on Beaver Divide, also known as Beaver Rim. This region is accessible from Jeffrey City by driving north along the Gas Hills district road, 14 miles north to Beaver Divide. At the divide, you will need to backtrack on a jeep trail that runs to the southeast for 1.5 miles (recommended maps - US Geological Survey, Rattlesnake Hills & Lander 1:100,000 topographic quadrangles).

Cedar Rim (Section 3, T31N, R95W). Fibrous chert and irregular beds of chalcedony occur in the Beaver Divide conglomerate member of the White River Formation along Beaver Divide (Love, 1970). The chert is found a few miles south of the Big Sand Draw oil field.

Muskrat Creek (section 20, T32N, R91W). Petrified logs are reported in the east-central part of section 20 near Muskrat Creek (B. Dunbar, personal communication to Sutherland, 1990).

Crooks Mountain Area (recommended maps - US Geological Survey, South Pass and Baroil 1:100,000 topographic quadrangles).

Bridger agates and wood. According to Love (1970), ostracod-bearing limestone, silicified green algae, fossil tree stumps, water-worn fragments of silicified wood, and dark-gray to brown agates are locally common in the Bridger Formation south of Crooks Mountain.

The Bridger Formation is exposed in the Cyclone Rim syncline (T26N, R96-97W) south of the Flattop Fault, on the Horsetrack anticline (NW T27N, R97W), and in a graben in the Bare Ring Butte area (sections 32 & 33, T27N, R92W). According to Love,"The formation consists of pale-green to blue-green and lemon-yellow siliceous bentonitic claystone and shale containing thin beds of ostracod-bearing limestone and green silicified algae".

Happy Spring (section 3, T28N, R95W). The type section of the Ice Point Conglomerate lies on the Happy Spring 1:24,000 Quadrangle at the site of the U.S. Coast Guard and Geodetic Survey triangulation station ICE (VABM 7466) on the northern flank of Crooks Mountain. According to Love (1970), many rounded fragments of black petrified wood occur in the Ice Point Conglomerate. The source of the wood is unknown; however, similar petrified wood is reported in the Bridger Formation (Pipiringos, 1961).

High-quality apple-green, pink, and black nephrite jade boulders were formally common in the vicinity of Ice Point, but the area is so highly prospected, that jade pebbles are now considered a rarity in this area (Love, 1970).

Great Divide Basin (recommended maps - US Geological Survey, Rawlins, Red Desert Basin, & Kinney Rim 1:100,000 topographic quadrangles).

Coal Gulch - Eight mile Lake (T17-18N, R93W). Petrified wood in a variety of colors has been found in this area along the road between Wamsutter and Baggs near the Continental Divide (Cheyenne Mineral and Gem Society, 1965; Johnson, 1973).

Delany Rim (T18N, R96W). An agate erroneously termed "Turritella agate" is found in this region, and actually is formed of silicified Goniobasis fossil snails (Hausel, 1986b). The rock is dominately brown to grey and is part of a silicified layer in the Laney Member of the Green River Formation. The Goniobasis are distinguished from Turritella gastropods by their freshwater habitat as well as shorter (usually less than 1 inch in length) and fatter appearence than the longer and thinner marine Turritella gastropods (Breithaupt, 1983).

The western part of this township is a good collecting area for the gastropods and other agates (Eloxite Corporation, 1971; Johnson, 1973). Three separate limestone units on Delany Rim are locally replaced by silica. The uppermost unit consists of Goniobasis chert, the middle unit consists of silicified algal heads, and the lower unit consists of oolitic limestone (Hausel and others, 1994).

Haystacks (T16-17N, R95-97W). The Haystack Hills are a source for several types of agate including petrified wood, oolitic agate, and petrified algae (Ralph Platt, personal communication to Sutherland, 1988). These agates appear to be associated with the Washakie Formation (Eocene). In this same region, areas underlain by the Laney Shale Member of the Green River Formation (Eocene) are a source for Goniobasis agate.

Ketchem Buttes (T15N, R89W). Ketchem Buttes, located 25 miles south of Rawlins, was explored in the 1950s for uranophane in the lower part of the North Park Formation (Miocene). Ketchem Buttes and the surrounding buttes were interpreted as remnants of paleo-hot springs as they are capped by travertine (Gordon Marlatt, personal communication to Hausel, 1993). The eastern-most butte contains silica bands in the form of red jasperoid that partially replaces sandstone and limestone (Hausel and others, 1994).

Miller Hill (T18N, R88-89W). Lovering (1972) reported jasperoid in the Miller Hill area about 25 miles south of Rawlins. The jasperiod was reported to be associated with localized concentrations of uranium ore. In this area, thin (3- to 10-foot thick) fresh-water limestone beds within the Browns Park Formation (Miocene) have been locally brecciated and replaced by silica. The silica was apparently leached from porous tuffaceous sandstones and precipitated in the limestone by groundwater.

Savory Creek prospect (section 32, T16N, R88W; and section 6, T15N, R88W). Five miles east of Ketchem Buttes in the Savory Creek area, some limestone has been completely silicified (Hausel and others, 1994).

Greater Green River Basin. The Greater Green River Basin of southwestern Wyoming includes the Great Divide, Washakie, and Green River Basins. Pertrified wood of the Eden Valley type, petrified algae, and Goniobasis agate are all found in this part of the State (Figure 71). Some jasperoids are also found on Aspen Mountain (Quaking Asp Mountain), and black flint and agate are associated with some buttes in the basin, including Black Butte and Aspen Mountain.

Many miles north of Aspen Mountain, Eden Valley petrified wood is found over a wide area centered around Farson. This petrified wood resembles ordinary weathered wood and has an opaque cream colored outer coating of silica over a core that varies from black to brown and grey, with grey streaks in darker specimens. Most of the material is smaller than a few inches in diameter and less than a foot in length (Sutherland, 1990).

Some specimens of the wood have been incompletely silicified. When these are exposed to weathering during long periods of time, the wood may loose its ability to take a high polish (Cheyenne Mineral and Gem Society, 1965). Because of this, lapidaries tend to search for choice quality material in recent exposures caused by erosion, or dig below the ground surface to find material.

The source of this material appears to be the Laney Shale Member in the upper part of the Green River Formation, and the overlying Bridger Formation both of Eocene age. During deposition of the Laney Shale sediments, which consist of tuffaceous, buff, chalky to muddy marlstone and brown to grey shale, the climate was warm and moist. Under these conditions hardwood trees, pine, fir, magnolia and other types of trees flourished in widespread heavily forested swampland cut by numerous braided streams. Lake Gosiute expanded and contracted in response to periods of increased percipitation followed by dry periods. The fluctuation in the lake level alternately allowed expansion of the forests around the lake, or drowned the timber as the lake rose. The drowned timber was gradually buried in lake sediments and showers of volcanic ash. Over time, the wood became petrified from the silica leached from the volcanic material. Later erosion exposed the silicified wood, silicified algae, oolitic limestones and layers of Goniobasis snail shells (Bradley, 1964).

The overlying Bridger Formation is primarily fluviatile with some thin lacustrine layers. Locally the formation contains silicified limestones and marlstones. Petrified wood is common in the Bridger Formation, particularly in the vicinity of Oregon Buttes (Bradley, 1964). Much of the wood is encrusted with algae and was silicified by processes similar to those petrified materials in the underlying Laney Shale. According to the Cheyenne Mineral Society (1965), this wood, known as the Bridger-type, consists of partially silicified black petrified wood. It includes limbs, trunks, stumps and roots. Where the wood is completely replaced by silica, it ranges in color from brown, tan to green. In addition to the wood, some clear chalcedony and vein moss agates are found in this region.

Reefs and beds of silicified Goniobasis gastropods, which were deposited only at certain depths within Lake Gosiute, are found throughout the area formerly covered by the prehistoric lake. Not all occurrences of Goniobasis were equally silicified. Some Goniobasis agates that are light-brown in color with a weathered appearance, do not take a good polish. The Goniobasis agates in shades of dark brown to black typically will polish, and this material is sought by rockhounds.

Big Sandy Reservoir (T27N, R105-106W). North of Farson and northeast of the Big Sandy reservoir, some Eden Valley petrified wood is found (Cheyenne Mineral and Gem Society, 1965). According to Gems and Minerals Magazine (July, 1976), some collecting localities for petrified wood and algae are located 1 to 2 miles east and north of the reservoir (recommended map - US Geological Survey, Farson 1:100,000 topographic quadrangle).

Black Butte (sections 4 & 9, T18N, R101W). Black Butte is capped by Erickson Sandstone (Upper Cretaceous). Grey to black flint and chert occur on Black Butte south of Point of Rocks (Hausel, Marlatt, Nielsen, and Gregory, 1995). Similar specimens of chert have been found elsewhere in the Greater Green River Basin. In particular, chert is found capping many sedmentary buttes in the basin since the chert acts as a resistant layer to erosion protecting the underlying sedimentary rocks (recommended map - US Geological Survey, Red Desert Basin 1:100,000 topographic quadrangle).

Blue Forest agate (sections 28, 29, 30, 31, 32 and 33, T24N, R110W). Petrified wood found in this region, has a black to brown central core surrounded by clear blue chalcedony producing an unique and very attractive, silicified wood (Figure 72) (Eloxite Corporation, 1971).

Within this same area, small, clear, symmetrical quartz crystals have been found that were eroneously termed ‘Wyoming diamonds’, similar to quartz crystals found in the Sweetwater agate beds in the Granite Mountains in central Wyoming (Sutherland, 1990) (recommended map - US Geological Survey, Farson 1:100,000 topographic quadrangle).

Blue beds petrified wood (T23N, R109W). The Cheyenne Mineral and Gem Society (1965) described the south half of this township as a source of several types of petrified wood, which are found in the “blue beds” that cover much of the area. These “blue beds” appear to be within the Bridger Formation (Sutherland, 1990), and are located a short distance to the southeast of the Blue Forest agate area (recommended map - US Geological Survey, Rock Springs 1:100,000 topographic quadrangle).

Cedar Mountain area (recommended maps - US Geological Survey, Firehole Canyon and Evanston 1:100,000 topographic quadrangle). The Cedar Mountain area offers an attractive place to collect rock and mineral specimens. The area is located in an isolated region of the State near the Utah border just north of the Uinta Mountains near Lone Tree. A variety of chalcedony, as well as beautiful pyrope garnet, and emerald-green chromian diopside and enstatite are found in this region, primarily in anthills on the Bridger Formation, in the Bishop Conglomerate, and in a cluster of breccia pipes of kimberlitic affinity.

Along the eastern flank of Cedar Mountain (sections 2 & 19, T14N, R110W; sections 22, 24 & 25, T14N, R111W; and section 23, T15N, R111W), Mitchell (1984) reported several varieties of chalcedony associated with the Bridger Formation. Agate, jasper, jasp-agate, flint, chert, and zebra flint (white, brown, and black striped flint) were found. Some of the material may be derived from the Bishop Conglomerate (Oligocene) which caps Cedar Mountain on the west and south. The jasp-agate in this region is red and yellow with white and blue streaks. The jasper is bright orange and yellow. Agates are multicolored to black with moss, flame, and plume patterns (Sutherland, 1990).

To the west of Cedar Mountain (T13N, R113W), outcrops of white beds in the Bridger Formation in the west-central and northwestern part of this township, exhibit occassional irregular bands of black and brown chert (Bradley, 1964). Along the western margin of the township (section 19, T13N, R113W), Madson (1983) reported silicified gastropods in the Bridger Formation. To the north in the vicinity of Leavitt Creek, Madson also reported silicified algae mats and found a fossilized turtle shell nearby.

Along the northeastern flank of Cedar Mountain (T15N, R111-112W), agates, chert, and jasper are found in soils derived from the Bridger Formation. Some of the better collecting areas are found near the center of these townships (W.D. Hausel, personal field notes, 1988).

Cumberland Flats (T19N, R117W). Some agate and pertrified wood is reported in the Cumberland Flats area south of Kemmerer (Johnson, 1973) (recommended map - US Geological Survey, Kemmerer 1:100,000 topographic quadrangle).

Fourmile Gulch (sections 2, 3, 8, 9, 15 & 16, T23N, R110W; and sections 34 & 35, T24N, R110W). Exposures of the Bridger Formation are reported by Mitchell (1982) to yield several varieties of chalcedony. These include yellow and brown jasper and petrified wood. Some of the wood and agates have a blue color, but the majority of the agates are multicolored (recommended map - US Geological Survey, Rock Springs 1:100,000 topographic quadrangle).

Granger area (T19-20N, R110-111W): Large concretions, known locally as geyser pipes, contain open spaced filled with quartz and calcite crystals. The rocks are found northeast of Granger on buttes in the area (Carolyn Jones, personal communication, 1996). Some of the concretions weigh several hundred pounds (Figure )

Hams Fork (T20N, R112-113W; and T21N, R112-114W). Abundant agate is found in the badlands along the Hams Fork. This area is underlain by extensive areas of Bridger Formation and the Laney Shale Member of the Green River Formation (Cheyenne Gem and Mineral Sociey; Sinkankas, 1959) (recommended map - US Geological Survey, Kemmerer 1:100,000 topographic quadrangle).

Jack Morrow Hills (sections 1, 2, 11 & 12, T25N, R103W). Eden Valley petrified wood has been collected in the area of the Hay Ranch in the Jack Morrow Hills (Cheyenne Mineral and Gem Society, 1965) (recommended map - US Geological Survey, Farson 1:100,000 topographic quadrangle).

Little America region (T18-19N, R108-111W). Goniobasis agate and some silicified algae are reported to cap some buttes between Green River and Granger (Hausel, 1986b; Sinkankas, 1959). The agate layers typically are found within the Laney Shale Member of the Green River Formation and the overlying Bridger Formation (Sutherland, 1990) (recommended map - US Geological Survey, Rock Springs 1:100,000 topographic quadrangle).

Lyman (section 1, T16N, R114W). ‘Moss Agate Cut’ lies on the Bridger Formation at this location. The source of the place name is unknown.

Moss Agate Knoll(section 1, T18N, R112W). Moss Agate Knoll is the place name at this locality which includes outcrops of the Bridger Formation (recommended map - US Geological Survey, Kemmerer 1:100,000 topographic quadrangle).

Quaking Asp Mountain (NW section 22, T17N, R104W). Banded jasperoids were discovered on Quaking Asp Mountain (also known as Aspen Mountain) south of Rock Springs (Hausel, Marlatt, Nielsen, and Gregory, 1995). Aspen Mountain has some unusual rocks and minerals which include alunite, travertine, free sulfur, silificifed breccia, kaolinite, and jasperoid. These are found within a 20 to 30 mi² silicified zone.

The Mountain is capped by a fine- to medium-grained sandstone and quartzite of the Rock Springs Formation (Upper Cretaceous), which is underlain by highly silicified, gray, silty and sandy shale interbedded with gray siltstone and fine-grained sandstone of the Blair Formation (Upper Cretaceous). These rocks are unconformably overlain by a sandstone facies of the Bishop Conglomerate. The jasperoids found near the top of Aspen Mountain, consist of dark- to light-grey banded agate with cross-cutting veins of quartz, and banded red, yellow-orange, and grey onyx-like jasperoid (Figure 73) (recommended map - US Geological Survey, Firehole Canyon 1:100,000 topographic quadrangle).

Sublettes Flat (T26-27N, R107W). Located west of Big Sandy Reservoir. This area is reported to host small limb casts of milky-white agate. The agates occassionally contain an internal tube-like structure and may exhibit an iris agate color display (Cheyenne Mineral and Gem Society, 1965) (recommended map - US Geological Survey, Farson 1:100,000 topographic quadrangle).

Whiskey Basin (T21N, R111W). Petrified wood and agate were reported in the Whiskey Basin area by Johnson (1973). This area is underlain by the Bridger Formation (recommended map - US Geological Survey, Rock Springs 1:100,000 topographic quadrangle). This area has had a long history of discoveries of petrified wood and other forms of chalcedony (Figure 74).

Oregon Buttes (T26-27N, R100-101W). An area east of Oregon Buttes is a source for much of the Eden Valley petrified wood (Sinkankas, 1959; Eloxite Corporation, 1971). The characteristic dark petrified wood found in this area, is probably a product of the Laney Shale Member of the Green River Formation, or the overlying Bridger Formation.

Oregon Buttes is the easternmost region from which large quantities of Eden Valley petrified wood have been reported. Bradley (1964) described petrified wood to be a common occurrence in the Bridger Formation, particularly in the vicinity of Oregon Buttes. He also reported silicified algal and oolitic limestone from the Laney Shale Member of the Green River Formation was found in section 2, T26N, R101W.

The area around Oregon Buttes is also a good place to search for gold, as considerable gold has been found in the region (Love and others, 1978) (recommended map - US Geological Survey, South Pass 1:100,000 topographic quadrangle).

Hartville Uplift (Recommended maps: US Geological Survey, Lusk and Torrington 1:100,000 topographic quadrangles). The Hartville uplift in southeastern Wyoming, is a favorite collecting locality for many rockhounds and private collectors (Figure 11). The uplift is enclosed by a core of Archean eugeoclinal metasedimentary and metavolcanic rock, with overlying Paleozoic sedimentary rocks that dip off the flank of the uplifted core.

Within the uplift, chalcedony is found in sedimentary rocks and in some veins. Multicolored, cryptocrystalline silica, mainly jasper, has been found in association with fractures and faults. The Guernsey Limestone (Mississippian) is a source of many agates and jaspers in the district, including red, purple, brown, and yellow jasper, as well as moss agate, stalactitic agate, and Youngite agate. Much of the collectable material occurs as float, however some is found as nodules, seams, and fracture fillings in the Guernsey Limestone. The Hartville Formation (Pennsylvanian-Permian) is also a source of jasper and fortification agate (Figure 75) (Sutherland, 1990).

Other attractive ornamental stones were described by the US Geological Survey (1903), which reported an attractive ornamental stone of blue quartz consisting of a brilliant coating of quartz crystals over blue to greenish-blue copper minerals (fibrous malachite with blue chrysocolla, on a pale-blue cupriferous allophane?) on hematite. This was reported at the Sunrise iron mine. Large masses of black dendritic agate with white coatings weighing up to 50 pounds (Slater agate?) were also reported in limestone. Some table tops were manufacture from this agate and exhibited at the World’s Columbian Exhibition in the late 1800s (US Geological Survey, 1893).

Adams Hartville agate mine (section 25, T27N, R66W). The Adams Hartville agate mine is located a short distance north of the town of Guernsey near the top of a hill in the center of section 25 (Eloxite Corporation, 1971). This appears to be at the same location as the Wilde and Deercorne mine referred to by the U.S. Geological Survey in 1908. The mine is responsible for most of the moss agate production from the Hartville area. The U.S. Geological Survey indicated that 2 tons of moss agate were produced in 1893, more than 7 tons in 1903, and 3.5 tons in 1908.

The agate varies from clear to white with black dendritic moss-like inclusions, and fluoresces bright-green under ultraviolet light. At this locality, the Guernsey Limestone contains some lower quartzite beds and rests unconformably on Precambrian (Archean) quartzites, phyllites, and schists (U.S. Geological Survey, 1908).

Moss agate mined around the turn of the century, was recovered from an irregular vein that varied from 1 inch to 2 feet thick and crosscut the Guernsey Limestone. Red banded agate has also been reported at this locality. About 200 yards north of the mine, some copper prospects were reported by Eloxite Corporation (1971) to contain brown jasper with bright blue streaks of chrysocolla.

Bassite. An attractive breccia formed of tan to light-grey limestone clasts cemented by red, pink, and purple chalcedony is found on the Gene Bass ranch (Norma Beers, personal communication).

Charter Oak mine (NE section 26, T28N, R65W). Samples collected from the Charter Oak mine included some jasperoid, as well as arsenopyrite, pyritized graphitic schist, and massive sulfide (Hausel, personal field notes, 1988). A few samples also contained malachite, chrysocolla, and chalcocite (Hausel, 1997).

Glendo Reservoir (T30N, R67-68W). Several varieties of agate and jasper are found on the shores of Glendo Reservoir and in the surrounding country (Hayford, 1971; Eloxite Corporation, 1971). These include a golden brecciated jasper, white stalactitic agate; red, pink, and white scenic seam (irregularly banded) agate; polka-dot agate, black moss agate, and butterscotch agate. The source for these materials is believed to be the Hartville Formation and Guernsey Limestone (Sutherland, 1990).

Guernsey Reservoir (sections 6, 7, 8, 9, 10, 15, 16, 17, 18, 19, 20, 21, 22, 26 & 27, T27N, R66W; and sections 1, 12 & 13, T27N, R67W). The shores and cliffs surrounding Guernsey Reservoir exhibit several varieties of chert and chalcedony which are often found as detrital material near the lake. These include red and purple jasper, youngite (Figure 76), and some fortification agates (Hayford, 1971).

Guernsey Youngite Cave (SE WW section 36, T27N, R67W). A cave, located in Guernsey Limestone, lies along the edge of the North Platte River, and is lined with Youngite agate. This cave is located on State land, and in the past was illegally mined for Youngite. The 10-foot-high entrance to the cave is located at the base of a 100-foot high cliff overlooking the Platte River, which in the past was accessed by wooden ladders.

The cave extends horizontally into the Guernsey Limestone for 600 to 1000 feet, and ranges in height from 1 to 15 feet. Much of the cave ribs and back is encrusted with pink to purple and grey youngite agate (named after a Dr. Young from Torrington). The cave is noteworthy because of its almost complete lining with silica. The source of the silica has been suggested to have been derived from leaching of former, overlying Oligocene White River Formation tuffaceous sediments (Sutherland, 1985).

Hell Gap (section 14, T28N, R65W). Three- to 5-foot wide veins containing jasper, east of Hell Gap, have been traced 850 feet along trend (Millgate, 1965).

McCann Pass (N/2 NE section 26, T28N, R65W). Jasper and jasperoid are found in the McCann Pass area (see also Charter Oak mine) (Hausel, personal field notes, 1988).

North Platt River (section 36, T 28N, R67W). Youngite is reported along the northern bank of the North Platt River north of the Guernsey Reservoir.

Page Flat (Center N/2 and SW NE section 36, T32N, R65W). Youngite is reported in the Page Flat area (R.E. Harris, personal communciation to Sutherland, 1990).

Rocky Pass (NE section 2, T27N, R66W). Northwest of Hartville, moss agates similar to the Sweetwater moss agates are found as float on the hill above the Hartville marble-onyx prospect. Some jasper is also present near the prospect (Eloxite Corporation, 1971).

Sawmill Canyon (SW NE NW section 22, T28N, R67W). Youngite is found on the southeast facing slope on the north side of the canyon (Sutherland, 1990).

Spanish Diggings (T30-31N, R66-67W). Fortification agates are reported in the vicinity of the Spanish Diggings (Eloxite Corporation, 1971). An orthoquartzite above the Morrison Formation (Jurassic) was locally a source for stone tools and weapons for Indians in the past (Sutherland, 1990).

NW section 5 & NE section 6, T28N, R65W. Brown chert nodules up to 1 foot in diameter associated with the Hartville Formation, are found in the nearby hills. When cut, these agate nodules exhibit colorful fortifications in bands of red to brown, white, grey, and clear (R.E. Harris, personal communciation to Sutherland, 1990).

Sections 6 & 7, T30N, R65W. Jasper is found in the Hartville Formation along a section line separating the two sections (R.E. Harris, personal communcation to Sutherland, 1990).

NE section 36, T28N, R65W & section 6, T27N, R64W. Some jasper, associated with faulting, is reported to the east of Garnet Hill. The jasper is porous. In the southeastern exposures, the jasper contains rare, small, molybdenite flakes (Millgate, 1965).

NW section 13, T27N, R66W. During field investigations in this area, samples of chrysocolla, banded chert, and jasper were found on a prospect pit dump. Common jasper and agate float were also found in the adjacent drainage. In this same area, umangite (Cu₃Se₂) was reported by Kerr McGee Corporation. Prospect pits in thr area are located along an unconformity between Precambrian dolomite and overlying Phanerozoic carbonate and conglomerate (Hausel, personal field notes, 1988).

NW section 24, T27N, R66W. Agate and jasper float are found east of Hartville Canyon (W.D. Hausel, personal field notes, 1988).

Sections 28, 33 & 34, T32N, R69W. Veins containing chalcedony with some associated uranium were reported by Guilinger (1956) in steeply dipping northeast-trending fault zones in the White River Formation (Oligocene). The chalcedony was reported to be radioactive, and to exhibit yellow-green fluoresence under short-wavelength ultraviolet light. Gruner (1955) noted that silificified fault zones in the southern part of the township formed discontinuous sharp ridges up to 30 feet wide. Some of these faults were reported to contain quartz as well as opal.

Laramie Mountains

Box Elder Canyon (sections 6 & 7, T32N, R74W; and sections 1 & 12, T32N, R75W). Located southeast of Glenrock near Highway 90. Layers of chalcedony and crystalline quartz have been reported in geodes in sandstones and limy sandstones in the Box Elder Canyon area (Osterwald and others, 1966; Hayden, 1871) (recommended map - US Geological Survey, Douglas 1:100,000 topographic quadrangle).

Casper Mountain (sections 17, 18, 19 & 20, T32N, R79W). Smoky quartz is reported in Precambrian pegmatite dikes on Casper Mountain (Harris and Hausel, 1986). In addition to the quartz, many of these pegmatites also contain rare to common, opaque, beryl crystals(recommended map - US Geological Survey, Casper 1:100,000 topographic quadrangle).

Duck Creek (sections 4, 5 & 6, T23N, R71W, and sections 35 & 36, T24N, R72W). Tiny amethyst crystals (less than 1 mm in length) were found in stream sediment concentrates during a diamond exploration project by the Wyoming State Geological Survey (Hausel and others, 1988). The nature of the study precluded recovery of any larger material; however, these small crystals suggest a possibility of larger crystals nearby upstream (recommended map - US Geological Survey, Rock River 1:100,000 topographic quadrangle).

Hay Canyon (W/2 section 18, T19N, R70W). Steeply dipping Paleozoic limestones along the east limb of Hay Canyon contain numerous agate and jasper replacements. These nodules range from red, grey, green to grey and typically are a few inches to several inches across. Some of the agates are highly fractured, although others are coheret fragments (Hausel, personal field notes, 1998) (recommended map - US Geological Survey, Rock River, 1:100,000 topographic quadrangle).

Moss Agate Hill (Section 23, T31N, R74W). Moss Agate Hill adjacent to Moss Agate Creek southwest of Douglas, has been a source of moss agate in past years. However, the hill has been essentially picked clean, and agates are now difficult to find (Osterwald and others, 1966) (recommended map - US Geological Survey, Douglas 1:100,000 topographic quadrangle).

Pinto Creek (sections 35, 36, T24N, R74W). Attractive, purple to light-blue chalcedony, agate, and botryoidal agate with a white crust is reported in the Pinto Creek area (Figure 77) (Norma Beers, personal communication).

South Cooney Hills (section 19, T23N, R69W). Massive white ‘bull’ quartz occurs in several pod-like veins in the east half of section 19 in the South Cooney Hills. The quartz is unimpressive in hand specimen, but has extraordinary piezoelectric properties. By striking the quartz with a hammer, a notaceable electric spark is generated within the quartz that is quite visible in a darken room. Some rose quartz is also found in the area, but with less developed piezoelectric display (R.E. Harris, personal communication to Sutherland, 1989) (recommended map - US Geological Survey, Rock River 1:100,000 topographic quadrangle).

State Line district (section 2, T12N, R72W). Some uncommon, well-formed, prismatic, iron-stained, translucent quartz crystals have been found in Precambrian pegmatites near Highway 287 south of Tie Siding (Hausel, 1986b). Several of the pegmatites in this area were quarried during the 1940s for feldspar (recommended map - US Geological Survey, Laramie 1:100,000 topographic quadrangle).

Leucite Hills

Steamboat Mountain (sections 9, 10, 11, 15 & 16, T23N, R102W). Agate and chalcedony were found on the slopes of Steamboat Mountain north of Superior, Wyoming (Sinkankas, 1959). Wilson (1965) further described the material as chalcedony-lined amygdules ranging in length from 3 to 6 inches. The amygdules occur within the vesicular phlogopite lamproite lava flows surrounding the Steamboat Mountain cinder cones (recommended map - US Geological Survey, Red Desert Basin 1:100,000 topographic quadrangle).

Medicine Bow Mountains (recommended map - US Geological Survey, Saratoga 1:100,000 topographic quadrangle).

New Rambler district (section 1, T14N, R79W, and section 6, T14N, R78W). A fault trending northeastly through the New Rambler district is marked by a narrow breccia zone. The breccia contains abundant, irregularly-shaped masses of blue-grey to white opaline chalcedony. At the New Rambler mine to the west (SW section 33, T15N, R79W), copper was interesected at shallow depths by a shaft that also exposed some “jaspilite”. The New Rambler mine is known for its variety of copper minerals and rare platinum mineralization (see Ore Minerals) (McCallum and Orback, 1968).

Rock Creek headwaters (section 31, T17N, R78W). Clear quartz crystals up to 1.5 inches in length and 0.5 inch in diameter, have been reported as isolated float in this area (Sutherland, 1990). The source of the quartz has not been identified.

Sheep Mountain (sections 5 & 8, T14N, R77W, and sections 20, 29 & 32, T15N, R77W). Large, log-like concretions which weather out from the Sundance Formation (Jurassic) along the western flank of Sheep Mountain are reported to contain small amounts of low-quality amethyst (Osterwald and others, 1966).

Powder River Basin. Within the Powder River Basin, are several varieties of chalcedony including petrified wood, chert and jasper that are associated with Paleozoic limestones along the eastern flank of the Bighorn Mountains (Hausel and others, 1990). Moss agates are also reported between Fort Reno and Crazy Woman Creek (Cheyenne Mineral and Gem Society, 1965).

The majority of the petrified wood found in the basin occurs in the Wasatch Formation (Eocene). Occassionally, some spectacular, large-diameter stumps and logs are found, such as the wood located east of Buffalo at the US Bureau of Land Management’s Dry Creek Petrified Tree site. Although occasionally impressive, this wood is typically poorly silicified, brittle, and easily crumbles into small pieces that are not suitable for tumble polishing.

Another type, the Crazy Woman Creek petrified wood, is more durable and well suited for lapidary purposes. This wood is well silicified, banded in shades of brown and white, and is found in terrace gravels about 60 to 120 feet above Crazy Woman Creek in an area extending from the flank of the Bighorn Mountains to where Dry Creek joins Crazy Woman Creek.

Large pieces of the Crazy Woman petrified wood, up to 18 inches in diameter and 16 inches long, were collected from the vicinity of Crazy Woman Creek in the past and can be found in landscaping and in local collections in Buffalo. Similar material has been found in terrace gravels along the Powder River near Kaycee (Sutherland, 1990).

Crazy Woman Creek petrified wood (S/2 section 24 & NE section 31, T 48N, R81W). Partially rounded cobbles of Crazy Woman Creek petrified wood ranging in length from 3 inches to more than 10 inches, have been found in piles of oversize material in a gravel pit in section 24. Chunks of the wood, up to 6 inches in length, have been found near an old gravel pit in section 31 (Sutherland, 1990) (recommended map - US Geological Survey, Buffalo 1:100,000 topographic quadrangle).

Poison Spider: Carnelian is reported between Poison Spider and South Casper Creeks west of Casper (Osterwald and others, 1966). Augey (1886) and the Cheyenne Mineral and Gem Society (1965) reported chrysoprase was also found north of Poison Spider Creek(recommended map - US Geological Survey, Casper 1:100,000 topographic quadrangle).

Shawnee Creek area (section 28, T32N, R69W). Fault zones east of Douglas, contain some quartz, chalcedony and opal (Gruner, 1955) (see also Opal) (recommended map - US Geological Survey, Douglas 1:100,000 topographic quadrangle).

McNeese Draw (sections 30 & 31, T51N, R80W). Numerous, poorly silicified, petrified trees and logs are found between the Healy and Walters clincker/coal beds in the Wasatch Formation (Eocene). The US Bureau of land Management maintains a withdrawn area in section 31 to allow visitors to see some impressive Early Eocene petrified forest remains. Durkin (1986) identified these trees as cypress and sequoia. Some specimens as tall as 12 feet, and 3 feet or more in diameter, have been found in this area (recommended map - US Geological Survey, Buffalo 1:100,000 topographic quadrangle).

T51N, R80-81W. East of Buffalo, Zeitner (1969) reported some amethyst-lined cavities were found in specimens of petrified wood(recommended map - US Geological Survey, Buffalo 1:100,000 topographic quadrangle).

Rawlins Uplift

Cold Spring Draw (sections 9, 10, 15, 16, 21 & 22, T22N, R88W). Carnelian agate is found along the Rawlins uplift in the vicinity of the headwaters of Cold Spring Draw north of Rawlins. The host for the agate is unknown (Harrison Cobb, personal communication to Sutherland, 1988) (recommended map - US Geological Survey, Rawlins 1:100,000 topographic quadrangle).

Saratoga Valley

Six Mile Hill - Sand Flats area (sections 1, 2, 3, 10, 11 & 12, T18N, R84W, and section 24, 25, 26, 27, 34, 35 & 36, T19N, R84W). Agatized wood and dendritic agates are found on the flats along Wyoming State Highway 130 north of Saratoga. The host rock appears to be tuffaceous sandstones, siltstones, and claystones of the North Park Formation (Miocene) (Sutherland, 1990) (recommended map - US Geological Survey, Rawlins 1:100,000 topographic quadrangle).

According to the Cheyenne Gem and Mineral Society (1965), agates have been collected along Wyoming Highway 130, 14 miles south of Walcott Junction. From Saratoga north to the Union Pacific railroad, the flats contain common agatized and opalized woods which fluoresce green under ultraviolet light.

Big Creek copper mine (NW section 9, T13N, R81W). Some of the best copper specimens of massive chalcocite and bornite that have been found in the state have come from this mine. The deposit was described by Houston (1961) to occur in a pink granite pegmatite. This pegmatite also contains common terminated quartz prisms. Much of the quartz is translucent, but specimens of excellent, transparent quartz similar to that found in Hot Springs County Arkansas are also found and relatively common (Ralph Platt, personal communication to Hausel, 1999) (see Trent Creek 1:24,000 scale topographic map for location). The Big Creek copper mine is erroneously listed as the Platt mine on the topographic map.

Seminoe Mountains. The Seminoe Mountains are primarily known for its gold veins and extensive banded iron formation; however, some jasperized banded iron formation cobbles and pebbles are commonly found in the area, particularly in the Deeweese Creek valley and also in paleoplacers along the northern flank of the Seminoe Mountains, extending from Deeweese Creek to east of Miracle Mile along the North Platte River.

Bradley Peak - Deweese Creek (sections 5, 6, 7, 8 & 18, T26N, R85W). Jasperized banded iron formation is found along the Deweese Creek valley north of Bradley Peak, and in unconsolidated conglomerates and colluvium extending along the northern flank of the Seminoe Mountains from Deweese Creek, east to the North Platte River (Hausel, 1994b). Specimens of the jasperized iron formation are magnetic and consist of alternating bands of black magnetite, dark grey quartz, and tawny to brown layers of jasper and grunerite (Figure 78).

This material has also been called taconite, jaspilite, and ironstone. Pebbles of the same material have been found a few miles to the east in the Miracle Mile area along the North Platte River (recommended maps - US Geological Survey, Baroil and Shirley Basin 1:100,000 topographic quadrangles).

Shirley Basin. The Shirley Basin forms a Tertiary basin flanked by the Laramie Range along its eastern and northern flanks. This basin is the source of several agates and jaspers, most of which have been derived from Casper Formation limestones and sandstones along the eastern margin of the basin. It has also been known for it fossil forests. In the 1930s, petrified logs, 3 to 4 feet in diameter, were commonly found in the Wind River Formation. Much of the material was removed between 1930 and 1950 (recommended maps - US Geological Survey, Laramie Peak & Shirley Basin 1:100,000 topographic quadrangles).

Boot Heel (Section 22, T26N, R77W). Several pieces of fossilized wood and tree stumps have been found on Boot Heel in the past (Nat Smith, personal communication, 1997). A circular topographic depression in this area was investigated by the WSGS. The origin of the feature was not determined. However, it contains abundant yellow, red, grey, black, and banded agate and jasper (Hausel, personal field notes, 1997).

Marshall (T26-27N, R75W). A diverse variety of agates are found near Marshall in the eastern part of the Shirley Basin. These include white moss agate, plume agate, black agate, jasp-agate, and others derived from Casper Formation limestones (Sutherland, 1990).

Mine Hills (Section 10, T26N, R75W). A reddish-brown jasper mixed with dark grey to black opaque agatized breccia is found in the Mine Hills and Crystal Hill area south of Marshall (Figure 3). This rock consists of pink breccia clasts of Casper Formation sandstone cemented with reddish-brown and massive black chert, coated with small grains of psilomelane (a metallic, manganese oxide). The psilomelane sparkels in sunlight (Hausel, personal field notes, 1988). Some agates from the area will fluoresce green under short- and long- wavelength ultraviolet light.

Moss Agate Reservoir (Section 32, T28N, R78W). Moss Agate reservoir is underlain by Wind River Formation (Eocene) sediments adjacent to Moss Agate Ridge which is capped by the White River Formation (Oligocene). The exact type and origin of the agates that gave rise to these names is unknown (Sutherland, 1990).

Specimen Hill (Section 19, T28N, R76W). A variety of agates have been found at Specimen Hill west of Little Medicine, including plume agate, banded black agate, dendritic agate, and jasper (Sutherland, 1990).

Solomon Springs area (sections 35 & 36, T24N, R74W). Clear to blue-grey and black, lightly banded, botryoidal agate and moss agate are found in the Casper Formation (Alan Hinman, personal communication to Sutherland, 1988). Some pieces are stalactitic with concentric banding, and others consist of reddish brown jasper (Sutherland, 1990).

Shirley Basin petrified wood (T27N, R78W). This township and the surrounding areas of Shirley Basin have been known as a source of petrified wood since the 1930s. Humid subtropical woods such as palms and other species once grew here, as demonstrated by a forest of silicified logs and fallen trees with diameters up to 3 feet or more in the Wind River Formation (Eocene). The majority of this wood was hauled away by commercial collectors between the 1930s and 1950s (Sundland, undated). The wood ranged in color from white to brown to black, and is generally of poor quality. Typcically, it breaks easily into small flakes. Harshman (1972) reported that the petrified forest area was located within sections 11, 12, 13, and 14.

Shirley uplift

Como Bluff (T22N, R77W). Silicified dinosaur bones have been found on both sides of Como Bluff, north of US Highway 287/30 near Medicine Bow (Sinkankas, 1959). A cabin constructed from some of the silicified bones lies adjacent to the highway. The Cheyenne Mineral and Gem Society (1965) reported that agatized wood fragments are also found on both sides of the Como Bluff anticline (recommended map- US Geological Survey, Medicine Bow 1:100,000 topographic quadrangle).

Agate Basin (sections 18, 19, T30N, R83W). Agate Basin is located on Oligiocene White River Formation 3 miles northwest of Alcova Reservoir (Sutherland, 1990). No other information is available (recommended map- US Geological Survey, Casper 1:100,000 topographic quadrangle).

Sierra Madre Mountains (recommended map - US Geological Survey, Baggs 1:100,000 topographic quadrangle).

Battle Lake (section 2, T13N, R86W, and section 35, T14N, R86W). Southwest of Battle Lake in the general area of Battle Creek and Baby Lake Creek, quartz crystals have been found in cavities and fractures in red granite. The quartz occurs as terminations on the granite, and are reported in a variety of colors, including amethyst, rose, smoky, milky white, and clear quartz crystals. Most are small and less than 2 inches in length (Platt, 1947).

Gold Coin mine (NE SW section 11, T15N, R87W). Clear to milky quartz crystals up to 3/8 inch in length, are found in a quartz vein near the Gold Coin mine (Sutherland, 1990). A milky quartz vein also contains galena, pyrite, chalcopyrite, and some gold and silver (Hausel, 1989).

Southeastern Wyoming. Southeastern Wyoming including the Laramie Mountains, Shirley Basin, Laramie Basin, Goshen Hole, and the Saratoga valley, extends as far west as the Rawlins uplift. This area contains several types of chalcedony including some petrified wood. The most common forms of chalcedony found in this region are agates and jaspers derived from Paleozoic limestones, particularly, from the Casper Formation (Pennsylvanian-Permian). Some of the petrified wood is probably silificified from silica derived from volcanic ash falls. The type of material found in this region is extremely varied in appearence, and includes several colors of jasper, jasp-agate, white moss agate, black agate or flint, and carnelian agate (Sutherland, 1990).

Farthing (section 28, T19N, R70W). In the Road Canyon area about 4 miles north of Farthing and 1/2 mile east of the road, clear polka-dot agates, crinoid stems embedded in jasper, and jasper thunder eggs have been reported (Hayford, 1971). The source of the material is unknown, although limestone from the Wells and Goose Egg Formations occur nearby, and may be potential sources (recommended map- US Geological Survey, Rock River 1:100,000 topographic quadrangle).

Iron Mountain (sections 22, 23, 26 & 27, T19N, R71W). Agates and jasper are found at Iron Mountain (Anonymous, 1976). According to Ralph Platt (personal communication to Wayne Sutherland, 1988), the source for the material is probably from a nearby limestone at Limestone Rim, which also contains some trilobites. The agates are similar in appearance to Dryhead agates (Sutherland, 1990) (recommended map- US Geological Survey, Rock River 1:100,000 topographic quadrangle).

Red Mountain (sections 16 & 21, T12N, R76W). Botryoidal agate and jasper were found around the base of Red Mountain (Muriel Forney, personal communication to Sutherland, 1988). These are derived from Casper Formation outcrops along the flank of the mountain (Sutherland, 1990) (recommended map- US Geological Survey, Laramie 1:100,000 topographic quadrangle).

Slater (T22N, R66W). Johnson (1973) reported dendritic agates from the hills near Slater were probably derived from either the White River Formation (Oligocene) or the Arikaree Formation (Miocene/upper Oligocene). Both formations contain tuffaceous material which may indicate a volcanic silica source for these agates (recommended map- US Geological Survey, Chugwater 1:100,000 topographic quadrangle).

Table Mountain (sections 25, 26, 35 & 36, T15N, R70W). Carnelian agate is reported near Table Mountain in the Silver Crown district (Aughey, 1886; Osterwald and others, 1966) (recommended map- US Geological Survey, Laramie 1:100,000 topographic quadrangle).

Wheatland Reservoir (NE section 3, T22N, R73W). Jasper and agate are found associated with the Casper Formation north of Wheatland Reservoir #2 (Hausel, personal field notes, 1983) (recommended map- US Geological Survey, Rock River 1:100,000 topographic quadrangle).

Wind River Basin. Several agates are found in the Wind River Basin. Attractive rainbow agates are reported along the Wind River near Riverton.

Lysite Area (recommended map - US Geological Survey, Lysite 1:100,000 topographic quadrangle).

Lysite (sections 30 & 31, T38N, R90W, and 35 & 36, T38N, R91W). An area immediately south of Lysite contains several varieties of agate including Goniobasis agate and petrified wood. The material occurs as float, some of which has been wind polished (Rohn, 1986).

Lysite Mountain (T40N, R90W). Agate is reported from Lysite Mountain (Johnson, 1973). The material is probably derived from Paleozoic limestones.

Crowheart Butte (T4N, R3W). Located east of Crowheart. Good quality petrified oak is found near Crowheart Butte (Ralph Platt, personal communication to Sutherland, 1990).

Fossil Hill (section 25, T32N, R101W). Clear to grey botryoidal to stalactitic agate was found in the Bighorn Dolomite, and as loose debris on slopes of Fossil Hill (Gary Glass, personal communication to Sutherland, 1990).

Wind River Mountains (recommended map - US Geological Survey, Lander 1:100,000 topographic quadrangle).

Beaver Creek (T30N, R100W). Jasperized and isoclinally folded banded iron formation, occur on a nob north of Beaver Creek and north of the Atlantic City iron mine (W. D. Hausel, personal field notes, 1998).

Dry Lake area (sections 8 & 9, T30N, R99W). Brownish yellow agates with black tree-like dendritic patterns known as Yellow Tree agates, were reported near South Pass by Spendlove (1984). These are partially carbonatized with an oxidized outer coating or surface (Sutherland, 1990).

Twin Creek (SW section 14, T30N, R99W). Irregulary banded, red and golded-yellow ‘flame’ jasper, is found associated with the Amsden or Phosphoria Formation in the Twin Creek area north of South Pass. The jasper takes a high polish and yields very attractive specimens (Figure 79) (Hank Hudspeth Jr., personal communication to Sutherland, 1990).

In the same region, a yellow to tawny moss jasper, known as ‘yellow tree agate’, is reported west of Highway 28 at the base of Limestone Mountain (approximately sections 7, 8, and 9, T30N, R99W). Samples of this material have produced some very attractive cabochons (Spendlove, 1984).

Cherry Creek (section 25, T31N, R99W). Agates associated with Jurassic rocks are found in this area near Highway 28 south of Lander. The area lies along the margin of the Wind River Basin adjacent to the Wind River uplift (Harris and others, 1985).

Sand Creek. Chrysoprase has been reported along the south side of Sand Creek. Sand Creek is a tributary of Beaver Creek located in Fremont County to the south of Lander (Cheyenne Mineral and Gem Society, 1965).

South Pass (T29N, R100W). Clear to milky and ferruginous quartz crystals have been found in some veins in the South Pass mining district along the southern tip of the Wind River Mountains (Sutherland, 1990). These crystals, however, are uncommon.

Yellowstone National Park

T56N, R111W. Amethyst and rock crystal fill voids in some petrified wood and wood casts in the vicinity of Amethyst Mountain in Yellowstone Park. These crystals are found over a wide area (Sinkankas, 1959). Upright petrified tree stumps area also reported in parts of the Eocene Lamar River Formation in the same area (Yuretich, 1984) However, no collecting of any kind is allowed within the boundaries of the National Park without a special research permit!