Dolomite

specimen number:
2102431

location:
Yellowstone Mine, Madison Co., Montana, USA

description:
Very choice large rhombohedral translucent crystals of dolomite measuring to 3.0 cm size forming a cluster without matrix. Choice large crystals for the species, in very good condition. These are not often seen available on the market today.

The Yellowstone mine, located in Madison County, Montana, is a historic underground talc quarrying and mining operation situated within the Ennis region. Geologically, the deposit belongs to the Archean-aged Cherry Creek Suite, where high-grade regional metamorphism altered ancient dolomitic marbles into extensive, high-purity tabular bodies of massive talc. Hydrothermal fluids circulating through fault zones reacted with the magnesium-rich carbonate rock, replacing large sections of the dolomite with white, pale green, and steatite-grade talc. Originally discovered and claimed in the early twentieth century, active commercial mining and quarrying operations began in earnest around 1951 under the Sierra Talc Company. The site underwent several corporate ownership shifts, operating steadily through the late twentieth century under Cyprus Industrial Minerals and later Luzenac America, and it remains documented as a major historic supplier of industrial-grade talc in the state.

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