Gypsum

specimen number:
8311373

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

description:
A very fine large cluster of gypsum crystals without matrix. This is excellent for this well-known locality. There are no points of attachment.

The Great Salt Plains, located near Jet in Alfalfa County, Oklahoma, is a unique geological site renowned for the occurrence of hourglass selenite, a distinct variety of gypsum. Geologically, the plains are a flat expanse of salt-encrusted silt and clay, where groundwater saturated with calcium sulfate rises to the surface through capillary action and evaporates. As the gypsum crystals grow within the saline mud, inclusions of sand and clay form a dark, permanent hourglass-shaped pattern inside the transparent crystals. Historically, the area was designated as a National Wildlife Refuge in 1930, but the tradition of collecting these crystals dates back decades through managed public digging areas. The site is the only place in the world where this specific hourglass formation is found, occurring in individual crystals and complex clusters. While there is no commercial mining or quarrying of the gypsum, the refuge operates a seasonal digging schedule, typically from April through mid-October, allowing thousands of visitors to hand-excavate these mineralogical curiosities from the shallow subsurface.

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