Colemanite

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Colorless bladed gemmy crystals of colemanite across the top of matrix. In good condition with very minimal cleaving present.The Kramer borate deposit, located near Boron, California, formed during the Miocene epoch within a shallow lake basin fueled by hot springs and late-stage volcanic activity. Over millions of years, massive layers of claystone and hydrated sodium borates accumulated, creating a highly concentrated geological structure. Historically, colemanite served as the primary commercial source of industrial boron following its discovery in Death Valley during the 1880s. In 1913, exploratory water well drilling near Boron struck colemanite, which prompted deeper prospecting that eventually uncovered even larger deposits of sodium borate minerals by 1925. These discoveries shifted regional mining operations away from underground colemanite extraction to massive open-pit mining of borax and kernite, transforming Boron into one of the largest borate-producing districts in the world.