Cryolite

specimen number:
2262240

location:
St. Peters Dome, El Paso Co., Colorado, USA

description:
Masses of cryolite throughout matrix. Interesting locality example for the species.

The St. Peters Dome district, located on the southern slopes of the Pikes Peak Massif in El Paso County, Colorado, is a globally recognized Western locality famous for producing rare alkaline halide assemblages, including notable masses of cryolite. Geologically, these unusual minerals occur within highly evolved, alkaline granitic pegmatites associated with the Proterozoic-age Mount Rosa intrusive complex. The cryolite formed as a primary pegmatite mineral during late-stage magmatic-hydrothermal crystallization, creating distinct, coarse-grained masses ranging in color from dull white to greasy gray. Over time, subsequent hydrothermal alteration by late-stage fluids broke down portions of the primary sodium aluminum fluoride, replacing it with a complex suite of secondary fluoride minerals including pachnolite, thomsenolite, gearksutite, and prosopite. Historically, prospecting in the district began in the late 1870s and 1880s, initially driven by searches for gold, silver, and kryolith, as the mineral was then spelled in early mining reports. Small-scale quarrying and underground mining were conducted sporadically from approximately 1880 through the 1910s at specific claims like the Eureka and Helen mines, where several tons of cryolite-bearing material were extracted primarily for scientific study and limited industrial testing. Large-scale commercial mining was never successfully sustained due to the localized, pocket-like nature of the ore bodies compared to the massive deposits in Greenland.

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