Continuation from Page 1
Barite, a complex parallel-growth crystal with multiple terminations, from a small isolated pocket; 7 by 5 cm. This was the largest gem-clear blue crystal collected.
Barite with white (opal-coated) calcite, pocket #2; 6 cm across, main crystal 5 cm high.
Barite cluster, pocket #1; specimen 8 cm high, crystals to 5.5 cm (the “V” specimen).
Barite on calcite, pocket #1; one of the largest single (parallel-growth) crystals found, 8 by 5 cm.
Barite cluster, pocket #2; specimen 7 cm high, crystals to 4 cm long.
Barite on calcite, pocket #1; 14.5 cm across, crystals to 6 cm long.
Barite cluster, pocket #1; 12 by 7 cm. Denver Museum of Natural History specimen #16349.
Barite with white (opal-coated) calcite, pocket #2; 7.5 cm across, main crystal 5.5 cm high.
Barite cluster, pocket #1; specimen 7.5 cm across, crystals to 7 cm long.
Calcite at Stoneham ranges from pale yellow to deep honey-colored; solid, inter-grown layers tend to appear a deeper brownish yellow. Distinct crystals of calcite form rhombohedra, sometimes modified or distorted, and typically 2-4 mm in size. Some of the calcite in pocket #2 appeared white rather than yellow, creating the visual effect of “snow” resting on the blue barite. The white color was later found to be due to a thin layer of rough-surfaced, microbotryoidal opal encrusting the calcite; the underlying calcite is the normal pale yellow color.
Calcite, 2-mm rhombohedral crystals. SEM photograph, 18x.
“White” calcite from pocket #2; 1-2-mm rhombohedral crystals coated with opal. SEM photograph, 35x.
X-ray diffraction indicates that the principal clay mineral in the host rock is montmorillonite. This clay mineral has formed through alteration by ground water of the glass shards in volcanic ash. The volcanic glass shards in this bed are nearly completely altered to clay, whereas most are quite fresh in the overlying beds.
Small amounts of opal are present as a late deposit on the surface of barite crystals and more commonly on calcite. The opal is most noticeable because of its fluorescence under UV radiation; brilliant green under short-wave UV, and faint green under long wave. The “white” calcite in pocket #2 appears as white as it does because of a thin layer of lustrous sparkling opal covering the calcite. The opal (nonprecious, with no opalescent colors) is colorless, glassy, and transparent; it can be termed hyalite. In a microscopic level it has a botryoidal morphology. The green fluorescence of hyalite opal is caused by traces of uranium as the uranyl ion, UO2+2, the presence of uranium in the Stoneham opal on calcite was confirmed by KEVEX EDX-XRF analysis.
Detail of botryoidal surface of opal coating on calcite; opal spherules are 50-100 microns. SEM photograph, 150x.
Stoneham barite can be suitable for cutting into gemstones as a specialty collector’s item; the Denver Museum of Natural History has 4.81- and 9.45-carat light blue stones from Stoneham in its collection, and the American Museum of Natural History has a 5.12-carat Stoneham barite on display in the Morgan Hall of Minerals and Gems (Modreski, 1989). Dennis Wilson has a 17.5-carat round-cut blue stone from barite he collected at Stoneham early in 1989 faceted by Jerrald Hess.
The 1989 excavation disturbed relatively little ground. The barite- and calcite-bearing fault zone was the only feature that was prospected. This fault was followed completely down to the contact with the Pierre Shale and – in the area of this excavation only – will probably not yield any specimen material in the future. However east of the excavation, the fault appeared to continue back into the hillside. This posed the problem of extensive overburden removal; it was therefore left undisturbed. The possibility exists that deeper into the hillside, along the continued intersection of the fault with the horizontal plane on which the two major pockets were encountered, still other unexposed pockets may exist.
Removal of about 21 meters of overburden would be necessary, a task for which equipment used on the 1989 dig would be inadequate. Minor pockets, of course, may exist at higher levels along the main fault zone or on subsidiary faults; other areas along the projected strike of the fault to the southeast and northwest might contain additional pockets nearer to the surface.
Many collectors over the years have dug by hand along the slope of the escarpment west of the present dig and have found generally small isolated pockets with individual or inter-grown crystals. This area is near or in the footwall of the projected trend of the fault zone, and barite crystal fragments are commonly found loose on the ground surface. New discoveries may come from this area.
About 45–90 meters to the north and east of the 1989 dig, a projecting “finger” of the ridge, composed of the Chadron Formation lying atop the Pierre Shale, extends to the northeast. This is an area that has produced fine barite specimens since the 1950s. It is suggested that toward the lower part of the Chadron clay beds, near the contact with the Pierre Shale, barite pockets may be more plentiful. A larger lobe of land, northwest of the 1989 dig and forming the western rim of the “blowout”, forms a low hill composed of the Chadron Formation. Some barite crystal float can be seen in parts of this area, but it has been little prospected by collectors.
Farther afield in this region of Colorado, there are many other possible areas for the occurrence of barite crystals in rocks of the White River Group: along both the north and south sides of the Pawnee Creek drainage, eastward and westward of the present site; and along other drainages running southward from the Chalk Bluffs and the Peetz Table, and bordering the South Platte valley. Workman’s thesis (1964a) describes over one hundred occurrences of barite crystals in eastern Weld and western Logan counties, eight of which he considered major localities.
The barite-producing areas near Stoneham extend for many square miles, and it is certain that many fine pockets will continue to be discovered in the future. The collecting areas on the Niklas Ranch are open and available to personal collecting, subject only to the restriction that the owners ask that prospective visitors check in at the ranch house for permission to enter the property.
Collector’s Edge Minerals, Inc. recognizes and thanks Rocks & Minerals for permission to use portions or all of their original article from the “Rocks & Minerals”, Volume 65, Number 3, pp. 202-222. Contributing authors were Peter J. Modreski, U.S. Geological Survey, Denver, Colorado; Bryan Lees CEMI, Golden, Colorado; and Dennis Wilson, Lakewood, Colorado.
Anonymous (1960). Colorado barite, The Mineralogist 28:110.
Belsher, D.R. and Baldwin, C.E. (1980). An Occurrence of barite at Hartsel, Colorado, Mineralogical Record, 11:23-25.
Bennett, N.L. (1986). The Stoneham barite locality, Colorado, Mineralogical Record, 17:255-258.
Bernstein, L.R. (1979) Coloring mechanisms in celestite, Amer. Min. 64:160-168.
Bershov, L.V.; Samoilovich, M.I.; Tarashchan, A.N.; and Martirosyan, V.O. (1969) Inorganic radicals in natural barium sulfate. Izvestia Akademii Nauk SSSR, Neorg. Mater. 5(6):1052-1056 [Chem. Abstracts, 1969, 71:155-156, 52102v.]
Bjorklund, L.J., and Brown, R.F. (1957) Geology and ground-water resources of the lower South Platte River valley between Hardin, Colorado, and Paxton, Nebraska. U.S. Geological Survey water-supply paper 1378.
Campbell, F.H., III, and Mitchell, R.S., Sand-calcite crystals from Stoneham, Colorado, Rocks & Minerals 36:18-21.
Clark, J. (1975) Controls of sedimentation and provenance of sediments in the Oligocene of the central Rocky Mountains. , in Geological Society of America memoir 144, pp. 95-117.
Cook, R. (1952) Colorado barite, The Mineralogist 20:364.
Cross, W. (1885) A list of specially noteworthy minerals of Colorado. Proceedings of the Colorado Scientific Society 1:134-144.
Dana, E.S. (18920 The system of mineralogy of James Dwight Dana, 6th ed. New York: Wiley.1961.
Dana, J.D., and Brush, G.J. (1884) The system of mineralogy, (11 sub-edition, with 3 appendices and corrections). New York: Wiley.
Denson, N.M. and Bergendahl, M.H. (1961) Middle and upper Tertiary rocks of southeastern Wyoming and adjoining areas. In U.S. Geological Survey professional paper 424-C, C168-C172.
Denson, N.M. and Chisholm, W.A. (1971) Summary of mineralogic and lithologic characteristics of Tertiary sedimentary rocks in the middle Rocky Mountains and the northern Great Plains, in U.S. Geological Survey professional paper 750-C, C117-C126.
Eckel, E.B. (1961) Minerals of Colorado: A 100-year record, U.S. Geological Survey bulletin 1114.
Eklund, R., Jr. (1965) Blue barite in Colorado! Rocks & Minerals 40:538-539.
Ellermeier, G.B. (1948) Blue barite near Sterling, Colorado, Rocks & Minerals 23:21.
Endlich, F.M. (1878) Catalogue of minerals found in Colorado, in Tenth annual report of the United States Geological and Geographical Survey of the Territories, embracing Colorado and parts of adjacent territories, e.. F.V. Hayden, 135-139, Washington, D.C.: Government Printing Office.
Epis, R.C.; Scott, G.R.; Taylor, R.B.; and Chapin, C.E. (1980) Summary of Cenozoic geomorphic, volcanic and tectonic features of central Colorado and adjoining areas, Colorado geology, ed. H.C. Kent and K.C. Porter, 135-156, Denver: Rocky Mountain Association of Geologists.
Fraas, E. (1901) Professor Fraas on the aqueous vs. Aeolian deposition of the White River Oligocene of S. Dakota, Science 14(5):210-212.
Galbreath, E.C. (1953), A contribution to the Tertiary geology and paleontology of northeastern Colorado, University of Kansas paleontological contributions, article 4.
Goldschmidt, V. (1913) Atlas der Krystallformen, Vol. 1. Heidelberg: Carl Winters Universitatbuchhandlung.
Hanor, J.S. (1968) Frequency distribution of compositions in the barite-celestite series, Amer.Min., 53:1214-1222.
Harben, P.W., and Bates, R.L. (1984) Geology of the nonmetallic, New York: Metal Bulletin, Inc.
Hofmeister, A.M. (1984) A spectroscopic and chemical study of the coloration of feldspars by irradiation and impurities, including water, Ph.D. diss., California Institute of Technology.
Hofmeister, A.M., and Rossman, G.R. (1985) A spectroscopic study of irradiation coloring of amazonite: Structurally hydrous, Pb-bearing feldspar, Amer.Min. 70:794-804.
Honess, A.P. (1923) Some interesting chalcedony pseudomorphs from Big Badlands, South Dakota, Amer. Jour. Sci., 5(5):173-174.
Kihm, A.J. and Middleton, M.D. (1980), Tertiary vertebrate biostratigraphy of Colorado, in Colorado geology, ed. H.C. Kent and K.C. Porter, 157-163, 157-163, Denver: Rocky Mountain Association of Geologists.
Lawler, T.B. (1923) On the occurrence of sandstone dikes and chalcedony veins in the White River Oligocene, Amer. Jour. Sci., 5(5):160-172.
Matthew, W.D. (1901) Fossil mammals of the Tertiary of northeastern Colorado, American Museum of Natural History, Memoirs 1:355-447.
Mitchell, R.S. (1960) Small barite nodules from Ovid, Colorado, Rocks & Minerals 35:9-11.
Modreski, P.J. (1989) Barite, a Colorado favorite, Colored Stone, Fall 1989 Show Guide 2(5):8-14.
Osborn, H.F. (1918) Equidae of the Oligocene, Miocene, and Pliocene, of North America; iconographic type revision, American Museum of Natural History, Memoirs 2:1-330.
Pearl, R.M. (1972) Colorado gem trails and mineral guide, 3d ed. Chicago: Sage Books/Swallow Press.
Randall, J.S. (1887) Minerals of Colorado, Georgetown: Georgetown Courier.
—- (1893) The minerals of Colorado [part 2, annabergite to cinnabar], State School of Mines Scientific Quarterly 2(2+3):117-136.
Samoilovich, M.I., and Lushnikov, V.G. (1969) Nature of the yellow coloring of calcite, Zap. Vses. Mineral. Obshchest 98(4):492-495 [Russ.; also Chem Abstracts, 1969, 71:459, 107305w].
Scott, G.R. (1978) Map showing geology, structure and oil ad gas fields in the Sterling 1o x 2o quadrangle, Colorado, Nebraska, and Kansas. U.S. Geological Survey miscellaneous investigations series map I-1092.
— (1982) Paleovalley and geologic map of northeastern Colorado, U.S. Geological Survey miscellaneous investigations series map I-1378.
Singler, C.R., and Picard, M.D. (1979) Petrography of White River Group (Oligocene) in northwest Nebraska and adjacent Wyoming, Contributions to Geology, University of Wyoming 18:51-67.
— (1980) Stratigraphic review of Oligocene beds in northern Great Plains, Wyoming Geol. Assoc. Earth Science bull. 13(1):1-18.
Smith, A. (1989) Celestite from Bull Creek, Travis County, Texas, Mineral News 5(4):1-2.
Smith, J.A. (1880) Catalogue of the principal minerals of Colorado, Biennial report of the state geologist of the state of Colorado, for the term ending Dec. 31, 1880, Denver: Tribune Publishing Co., pp. 42-74.
— (1883) Catalogue of the principal minerals of Colorado, Report on the development of the mineral, metallurgical, agricultural, pastoral, and other resources of Colorado for the years 1881 and 1882, Denver: Tribune Publishing Co., pp. 127-149.
Voynick, S. (1988) High plains barite, Rock & Gem 18:36-41.
Wanless, H.R. (1922) Lithology of the White River sediments, Amer. Phil. Soc. Proceedings 61:184-203.
— (1924) The stratigraphy of the White River beds of South Dakota, Amer. Phil. Soc. Proceedings 64:190-269.
Workman, W.E. (1963) Sheaflike barite from New Raymer, Colorado, Virginia Jour. Of Sci. 14:243-244.
—(1964a) Barite from the White River Formation of northeastern Colorado, M.S. thesis, University of Virginia.
—(1964b) Barite from the White River Formation of northeastern Colorado, Virginia Hour. Of Sci. 15:335-336.