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 Wyoming has been cloudy and translucent 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 field partner, Wayne Sutherland, who provided considerable library research on this subject when I was at the Wyoming Geological Survey and spent time in the field searching for mineral deposits. Wayne and I had a great time working together and wrote a book on World Gemstones that you cam call the Wyoming State Geological Survey for a copy at 307-766-2286. (Hausel, W.D., and Sutherland, W.M., 2006, World Gemstones: Geology, Mineralogy, Gemology & Exploration: WSGS Mineral Rept MR06-1, 363 pages). This book was never formally published.
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| Variety of agates found in Wyoming |
The chalcedony deposits 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.
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Wiggins fork fossil wood
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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. These are only two of the many attractive specimens of chalcedony found in Wyoming.
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, 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).
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.
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| The GemHunter and Wayne Sutherland in the field. Except when the earth was covered in snow, we were always in the field. This is one of the reasons we discovered so many mineral deposits in Wyoming. Only Ray Harris (RIP -Ray was harassed to death by the WGS director) out uranium research geologist for the WGS, spent time in the field and also made discoveries. The rest of our geological staff didn't like getting dirty and pretty much stayed at home. |
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 that 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.
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| Sweetwater moss agates from the Cedar Rim opal field near Riverton |
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).
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| Banded Tin Cup Japser. |
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).
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| Jasperoid cabochon from Quaking Asp Mountain |
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).
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| brecciated jasper from the Tin Cup district. |
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 (Hausel, personal field notes, 1988). The amethyst appears to be rare, but its presence suggest other sources should occur in the district. This was the first verified discovery of amethyst in this area.
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, opal, minor copper, spodumene, apatite, tourmaline, and corundum have all been found in the Granite Mountains.
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| The Granite Mountains are known for jade. |
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).
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| Wayne Sutherland looks at massive jasper at Jasper Hill in Dry Creek area of the Rattlesnake Hills. Some material collected here by the author contained actually imprints of fossil leaves indicating that this was at one time a jasper goo likely erupted from a hot spring. |
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).
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| Sweetwater agate (20.98 carats) from the Granite Mountains. |
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.
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| Lost Muffler Jasperoid |
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. 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).
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| I'm standing in an old gold prospect surrounded by many tons of high-quality jasper in the Tin Cup district. |
Sutherland-Red Boy mines (sections 25 & 36, T31N, R93W). The Sutherland shaft (no relation to Wayne Sutherland that we know of) 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).
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| Wayne points to old shaft at Tin Cup while standing on a tailings pile of jasper. Behind this is another tailings pile of jasper and further behind along the ridge is another tailings pile of jasper, with others on the back side of the hill. In between are likely thousands of tons of jasper along a shear zone buried beneath a few inches of soil. |
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. 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.
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| Black flint (zebra flint) from Green River Basin |
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 (Eloxite Corporation, 1971).
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| Blue forest agate (courtesy of Wayne Sutherland) |
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.
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| Pyrope garnet, chromian diopside and chromian enstatite from Green River Basin anthills. Diamonds have also been found in this area. |
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.
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).
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| Jasperoid discovered by the author on Quaking Asp Mountain. |
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 (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. 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.
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| 8.17-carat jasper cabochon cut from Hartville material. |
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).
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| Youngite from Hartville |
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.
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| Folded BIF from Bradley Peak (Hausel, 1994) |
Bradley Peak (sections 5, 6, 7, 8 & 18, T26N, R85W). Jasperized banded iron formation is found along the flanks of the Seminoe Mountains derived from outcrops of spectacularly folded banded iron formaton along the flank of Bradley Peak, and in unconsolidated conglomerates and colluvium of the Miracle Mile paleoplacer (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.
This material has also been called taconite, jaspilite, and ironstone. Pebbles of the same material have been traced to the Miracle Mile area along the North Platte River where the author along with Charlie and Donna Kortes collected several dry sediment samples and panned out gold and diamond indicator minerals. The gold likely is derived from the Bradley Peak area and the indicator minerals from unknown sources (recommended maps - US Geological Survey, Baroil and Shirley Basin 1:100,000 topographic quadrangles).
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| Jasperized banded iron formation cobble paper weight collected in the paleoplacer north of the Seminoe Mountains. Bands of limonite, jasper and magnetite form much of this rock. |
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. 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 appearance, 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!
