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Hourglass Selenite Crystal

Oklahoma State Crystal

Hourglass selenite crystals; photo courtesy of USFWS.

Official State Crystal of Oklahoma

Oklahoma designated the unique hourglass selenite crystal as the official state crystal in 2005 after elementary school students from Bryant and Red Oak School petitioned the state legislature. All State Minerals & Rocks

Hourglass selenite crystals are found only on the salt plains of Oklahoma, a unique 11,000-acre geological area. The salt plains were formed by repeated flooding by sea water millions of years ago.

Selenite (hydrous calcium sulfate) is a crystallized form of gypsum, a common mineral in sedimentary environments that can take on a great variety of crystal forms and shapes. Crystals take on the characteristics of their environment - iron oxide in the soil gives the hourglass crystals their chocolate brown color.

On the salt plains, sand and clay particles often form an "hourglass" shape inside the crystal. Crystals measuring up to 7 inches long have been found, along with complex combinations weighing as much as 38 pounds.