Thenardite

specimen number:
2354163

location:
Soda Lake, San Luis Obispo Co., California, USA

description:
A cluster of gray semi lustrous slightly translucent crystals of thenardite measuring to 3.0 cm in size with little attached matrix. In good condition, very good example for the species.

Located in the Carrizo Plain of San Luis Obispo County, California, Soda Lake is an endorheic alkali lake basin formed by structural faulting along the San Andreas Fault Zone. Evaporation of mineral-rich runoff trapped within this closed drainage system leaves behind extensive surface crusts of sodium sulfate evaporites. Native Americans and early pioneers gathered these saline salts, but commercial extraction remained minor compared to larger evaporite operations elsewhere in the state. Soda Lake is well known to mineral collectors for producing pale yellow to colorless crystals of thenardite, an anhydrous sodium sulfate mineral that precipitates directly from concentrated brine during warm dry seasons. Because thenardite rapidly dehydrates or converts when exposed to humidity, field collectors must carefully preserve these delicate tabular crystals, which are preserved today within the protected boundaries of the Carrizo Plain National Monument where mineral collecting is restricted.

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