Left - Barite rose showing cluster of barite crystals that produce a rose-like appearance. Below – cleavage in barite (linear fractures within the crystals).
Barite crystallizes in the orthorhombic crystal system and may form aggregates or divergent groups of tabular crystals known as ‘barite roses’. These extraordinary crystal aggregates have a very pleasing appearance and often are sought by mineral collectors.
Barite has perfect basal cleavage with prismatic cleavage at right angles to basal cleavage, and will sometimes form white masses exhibiting distinct right angle prismatic cleavage. Tabular white, yellow, grey, blue, red, or brown, opaque, translucent and transparent crystals have been reported.
Some of the more attractive specimens found in Wyoming are light aquamarine blue, transparent to translucent, thin tabular crystals compressed along the c-crystallographic axis. This compression produces distinctly large crystal faces. The individual crystals of the Wyoming aquamarine blue barite occur as plates with distinct beveled edges. Perfect basal cleavage parallel to the c-axis lies perpendicular to imperfect prismatic cleavage parallel to the b-axis. Where found near the Mine Hills the Shirley Basin of southeastern Wyoming, the barite occurs in vugs in limestone enclosed by calcite and prismatic quartz.
The blue barite from Shirley Basin shows crystals with beveled edges along the edge of the a-axis. Note the beveled edge on the crystal in the center of the photo.
Shoshone Canyon (SE section 5, T52N, R102W). Small radial clusters of white barite crystals are found in the Shoshone Canyon area of Rattlesnake Mountain about 4 miles west of Cody in northwestern Wyoming. Some of the crystals from in this area are reported to be one inch in length. This barite is associated with paleo-hot spring deposits and solution cavities in the Mississippian Madison Limestone.
Hog Park (NW section 2, T12N, R85W). A pod-like mass of barite, 40 feet wide by 300 feet long is reportedly associated with opal in the Hog Park area of the Sierra Madre Mountains several miles southwest of Encampment. The barite is reported to occur along the northern edge of a shear zone in contact with red quartz monzonite. When I investigated this deposit, I could not find any evidence of opal, but white crystalline to massive barite was present.
Shirley Basin. White barite concretions are reported in Shirley Basin northeast of the town of Medicine Bow. These are weakly fluorescent under long-wavelength ultraviolet light.
In addition to white barite, very attractive aquamarine blue barite crystals occur in the vicinity of Sheep Creek near Crystal Hill adjacent to the Mine Hills (section 10, T26N, R75W) along the southeastern margin of the basin and adjacent to the western flank of the Laramie Range. Mine Hills are located on the Laramie Peak 1:100,000 topographic map and are accessed from the west from Shirley Basin (see also Shirley Basin 1:100,000).
The barite occurs as attractive light-blue, transparent to translucent, tabular crystals and is found with calcite and quartz in vugs in the Casper Formation near a massive psilomelane, manganite (manganese) and jasper replacements in the Casper Formation (Hausel and Sutherland, 2000).
References
Dana, E.S., and Ford, W.E., 1949, A textbook of Mineralogy: John Wiley & Sons, 851 p.
Hausel, W.D., and Sutherland, W.M., 2000, Gemstones and other unique minerals and rocks of Wyoming: Wyoming Geological Survey Bulletin, 267 p.
Sinkankas, J., 1964, Mineralogy: Van Nostrand Company, 585 p.
