Gypsum

specimen number:
8311488

location:
Great Salt Plains, Jet, Alfalfa Co., Oklahoma, USA

description:
Good thumbnail sized cluster of gypsum crystals. No points of attachment and in very good condition. This is classic material for this locality.

The Great Salt Plains, situated within Alfalfa County in northern Oklahoma, United States, represents a globally unique mineral locality celebrated for producing highly unusual, hourglass-shaped crystals of selenite gypsum. Geologically, this immense, flat expanse is a salt marsh formed within a low-lying quaternary alluvial basin, where saline, mineral-rich groundwater continually migrates upward through Permian-age bedrock by capillary action. As the shallow water evaporates on the surface, it leaves behind a thick crust of halite, while just a few inches beneath the mud, the brine supersaturates with calcium sulfate, causing crystals of selenite gypsum to precipitate directly inside the sandy clay matrix. This specialized environment allows fine grains of sand and clay to become trapped in an hourglass pattern inside the growing crystals during formation, creating a distinct, dark brown internal shadow that is found nowhere else on earth. Historically, the area was long utilized by indigenous tribes and early pioneers as a vital source of surface salt, but the unique crystalline gypsum deposits gained formal scientific and public interest during the twentieth century, leading to the establishment of the Great Salt Plains National Wildlife Refuge by the federal government in 1930. While commercial mining or quarrying of the gypsum has never been permitted due to strict environmental protections for migratory waterfowl, the United States Fish and Wildlife Service has operated a highly regulated, seasonal public digging area at the refuge for decades.

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