Buena Vista Gem Works noted that in Nebraska the area of collecting is north of US 20 from Chadron to the Wyoming state line, generally following outcrops of the Chadron. Major collecting localities in Wyoming include Lance Creek and Hat Creek southwest and reasonably close to the Hills and Glendo and Guernsey further to the south.
Pabian and Cook reported Fairburn-type agates at localities along the east-flowing Platte River in Nebraska. Most agate hunters describe Fairburns as fortification agates with a holly leaf banding. They have sort some of red to orange banding due to iron oxides with the black banding ascribed to manganese.
It seems well established that the agates out on the South Dakota plains originated in the Minnelusa Formation of Pennsylvanian-Permian age and were transported away from outcrops in the Black Hills by Cenozoic streams. Perhaps the best-know site for observing in situ Fairburn agates is at Teepee Canyon west of Custer see blog posting Map showing location of Hartville Uplift in eastern Wyoming. Map from Dickinson and others, I find it interesting that Fairburn-type agates found at the Glendo and Guernsey locations in southeastern Wyoming most likely came from rocks similar to the Minnelusa Formation Hartville Formation exposed around the perimeter of the Hartville Uplift Sutherland, This uplift is a Laramide structure, not unlike the Black Hills with which it connects on the north, but much more topographically and structurally subdued.
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Denver mineral show report fall part 3. Denver mineral show report fall part 4. Denver mineral show report fall part 5. This wood is silicified, banded in shades of brown and white, and found in terrace gravels about 60 to 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.
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, 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, Banded Tin Cup Japser.
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.
This wood resembles ordinary weathered wood and has an opaque cream colored coating of silica covering a silicified black to brown core. 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. The wood has a black to brown central core surrounded by clear blue chalcedony which producing an unique and very attractive, silicified wood. 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. Some of these will produce beautiful lapidary stones Hausel and Sutherland, 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 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, 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, 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.
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, 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, Jasperoid is reported in Paleozoic sedimentary rocks in the western part of this township Nelson and others, ; Hausel, 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 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, Nodular fortification agates occur along outcrops of the Phosphoria Formation along the southern and eastern flanks of the Pryor Mountains.
Dryhead agate T58N, RW. 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, 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, recommended map - US Geological Survey, Powell , topographic quadrangle.
Moss agate, chalcedony, and chert are found in Paleozoic limestones near Spanish Point Sutherland, Root , described this agate as a brown- to cream-colored moss agate. Dendritic agates were found on the Jack No. Limb cast agates are found along the Bighorn River Keenan, ; Johnson, These agates are grey to white and are similar to the Wiggins Fork wood found many miles west in the Absaroka Mountains Sutherland, 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, 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, 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, Locally, samples contain bright waxy, yellow-orange specs of wulfenite, massive galena in limestone breccia with some minor fluorite Hausel, c see also Ore Minerals.
Mineral Hill district. Veins and pods of jasper and jasperoid are found in the Deadwood Formation Cambrian in an semicircular outcrop around Mineral Hill Welch, 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. 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, 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. 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.
The Granite Mountains are known for jade. 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, Clear chalcedony balls found in the region, are sometimes coated with opal and white ash.
Love 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 , topographic quadrangles.
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 mi 2 Love, These agates have also been reported in gravels many miles down stream Sutherland, Agate Lake.
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, 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, 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.
Johnson reported agates from the Crooks Gap area south of Jeffrey City. A 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, Some of these agates fluoresce yellow under ultraviolet light Sutherland, 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 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, The agates have been quarried for lapidary use in the past Sutherland, Moss agates are found both upstream and downstream from Highway , where the highway crosses the Sweetwater River in the vicinity of Sweetwater Station Johnson, ; B. Dunbar, personal communication to Sutherland, Sweetwater agate 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 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 Love, These extend east into the next two townships. The agates are rounded, and vary from 0. The agates vary from translucent brown to grey and a few have moss-like inclusions Love, Fossil wood is also found nearby in the Moonstone Formation Sutherland, Within the area around Diamond Springs Draw, small, clear, quartz crystals were at one time relatively common in the Sweetwater agate beds.
However, they are quartz rather than diamonds. This terrane consists of an Archean greenstone belt fragment intruded by Tertiary alkalic igneous rocks. The area has high-potential f or the discovery of large-tonnage commerical gold deposit s, and contains several jasperoids and breccias in vein-like deposits known as exhalites Hausel, e. Agates are also found in the pediment gravels along the southern margin of the district. This mineralized zone consists of a cherty unit associated with jasperoid, quartz, graphitic schist, and local pyrite, minor galena and arsenopyrite.
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. 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 , and Rattlesnake Hills , 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.
Thermopolis, mines in area to SW. Thermopolis, in bluffs to W. Sportman Lake, prospect 1 mi. Como Ridge, N of US Rambler Mine, near Holmes Campground.
Grand Encampment, many area mines. Jelm Mountain, S side area mines. Laramie, outcrops 5 mi. Laramie Mountains, draws and washes of eastern slopes. Red Buttes, deposit in area to S. Seminoe Reservoir, all area draws and washes. Baggs, area mines to W. Creede Mine, near Encampment. Sierra Madre, area mines. Shirley Basin, N of Medicine Bow. Saratoga, area draws and washes N to Walcott. Converse County, many area mines in SW. Deer Creek Canyon Mine.
Box Elder Canyon, near Glenrock. Moss Agate Hill, near Douglas. Warren Peak, area mines. Copper Prince Mine. Black Hills National Forest, area mines. Jay Em, area draws and washes. Buffalo, area to NE along US Crazy Woman Creek, general area E of Buffalo.
Copper King Mine. Chugwater Creek, in gravels. Sage Hen Creek, in gravels. Sweetwater River, area E of Split Rock. Casper, area quarries. Casper, pegmatite outcrops to S. Poison Spider Creek, area washes and draws. Hartville, area washes and draws to W.
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