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Ulexite

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What they call clamshell ulexite, a compact fibrous crystal grouping without matrix. In good condition.Located in Kern County, California, the U.S. Borax Mine at Boron is situated within a Miocene lacustrine basin where ancient thermal springs discharged high concentrations of sodium and boron into trapped lake waters. Over time, thick beds of hydrated sodium borate minerals crystallized under evaporative conditions within claystone strata. Open-pit mining began in the 1950s, transforming the locality into one of the largest surface borate deposits in the world. Beyond its massive commercial output, the mine became world-famous among mineral collectors for producing unique ulexite formations known as clamshell ulexite. These distinctive specimens feature silky, radiating fibrous ulexite crystals that formed inside curved fractures and spaces within the surrounding lacustrine clay, creating natural bivalve-like nodular shapes that resemble small clam shells.