Sulphohalite

specimen number:
2282042

location:
Searles Lake, San Bernardino Co., California, USA

description:
A choice loose octahedral crystal without matrix. In great condition all around. Choice thumbnail for the species.

Searles Lake, situated in the northern Mojave Desert of San Bernardino County, California, is a massive evaporite playa renowned for its incredibly diverse and complex assemblage of saline minerals. Geologically, the lake is an endorheic basin that collected mineral-rich runoff from the Sierra Nevada mountains during successive glacial pluvial periods throughout the Pleistocene epoch. As the water evaporated over thousands of years, it left behind a series of thick, layered, subterranean salt beds interleaved with mud layers, creating a deep reservoir of highly concentrated, alkaline brines rich in sodium, potassium, borate, carbonate, sulfate, and chloride ions. Commercial harvesting of these resources began in 1873 when John W. Searles and his brother started extracting borax using primitive wood-fired crystallization vats. The operations evolved dramatically into sophisticated, continuous industrial chemical complexes run by various companies over the next century, including the American Potash and Chemical Corporation and modern operators, processing thousands of tons of potash, soda ash, and borates daily from the late 19th century through to the present day.

Sulphohalite is an unusual sodium sulfate-chloride-fluoride mineral that crystallizes in the isometric system. Geologically, it forms almost exclusively as an authigenic precipitate within highly advanced, alkaline evaporite lake deposits, where it crystallizes directly out of concentrated brines under specific conditions of high salinity and cold temperatures. The mineral generally occurs as distinct octahedral or dodecahedral crystals, as well as granular masses, which range from colorless and transparent to white, pale yellow, or light green with a vitreous luster. It is particularly notable for containing three distinct anions (sulfate, chloride, and fluoride) within a single, stable crystal structure.

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