Searching for Selenite

The Great Salt Plains in Oklahoma occupy a roughly triangular area surrounded by agricultural fields. Several streams run through an expanse of bright salt that covers the western side, and a lake with green-tan water fills the eastern corner behind a dam.

October 10, 2025

Dating back centuries, salt-crusted plains in present-day Oklahoma held great value to native tribes and, later, to homesteaders. People used the inland supply of salt in their diets, for tanning deer hides, and for trade. The area also proved to be a fertile hunting ground due to the abundance of game that sought out the nutrient-rich habitat.

Since 1930, the salty deposit located about 90 miles (150 kilometers) northwest of Oklahoma City has been part of Salt Plains National Wildlife Refuge. Today, the plains are still known as a gathering place for diverse animal life, including more than 300 species of birds. But its salt resources have become appealing in another way: it is the only place in the world where people can dig for a distinctively patterned form of crystallized gypsum.

The OLI (Operational Land Imager) on Landsat 8 captured these images of the area in natural color (above) and false color (below) on October 10, 2025. The salt basin is partially filled by Great Salt Plains Lake, a shallow reservoir formed by the damming of the Salt Fork Arkansas River and fed by ephemeral streams.

The false-color image combines the shortwave infrared portion of the electromagnetic spectrum with visible light (OLI bands 7-4-2). In this combination, healthy vegetation appears dark red to purple, and water is blue. The variation in color on the salt plain may be due to different moisture or salinity levels. (Scientists can use shortwave infrared data in estimations of soil salinity.)

In a false-color satellite image of the Great Salt Plains in Oklahoma, salt-crusted areas appear white to light blue and lake water is dark blue to green. Surrounding agricultural areas range from dark purple to light orange.

October 10, 2025

The basin’s salt has its origins in the Permian Period, about 300 million to 250 million years ago. A shallow salt layer from that time still underlies parts of the southwestern U.S., including western Oklahoma. Salt gradually dissolves into groundwater, and when the resulting brine rises to the surface, the water evaporates and leaves behind a bright crust.

The saline water is a key component in a mineral structure unique to the area—hourglass selenite crystals. Selenite, a crystalline variety of gypsum, forms in the top two feet of the wet subsurface when saline water combines with gypsum. The process can occur relatively quickly when temperatures and moisture levels are right. Likewise, crystals may dissolve away if the environment is too wet. Sand and clay particles get incorporated into the otherwise clear crystals, often in a brownish hourglass shape.

Visitors to the Salt Plains scour for these crystal “blades,” but crystal collecting is limited to certain months of the year so as not to disrupt seasonal activities of shorebirds and waterbirds. The salt flats provide habitat and feeding grounds for species such as the snowy plover, sandhill crane, and endangered whooping crane. Other wildlife common to the area include white-tailed deer, red-eared sliders, and nine-banded armadillos.

NASA Earth Observatory images by Michala Garrison, using Landsat data from the U.S. Geological Survey. Story by Lindsey Doermann.