Gypsum

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Neat double terminated hourglass gemmy crystal of gypsum. In great condition all around. Classic material for this locality. The Great Salt Plains, located in Alfalfa County, Oklahoma, is a unique geological environment consisting of a flat expanse of salt-encrusted silt and clay. Geologically, the plains are part of the Anadarko Basin, where ancient Permian-aged seas left behind thick evaporite deposits of salt and gypsum. The site is world-famous for the growth of hourglass selenite, a variety of gypsum that forms just beneath the surface as groundwater enriched with calcium and sulfate crystallizes, trapping brown clay in an hourglass shape. Historically, mining and quarrying activities for salt were documented as early as the 1800s by explorers and Native American tribes, but industrial production was largely overshadowed by the establishment of the Salt Plains National Wildlife Refuge in 1930. While commercial mining is no longer a primary focus, the area has remained open to the public for regulated crystal digging for decades, making it a premier locality for amateur mineralogists. Today, the Great Salt Plains serves as a critical habitat for migratory birds and a fascinating laboratory for studying modern evaporite crystallization processes.