Gypsum outcrop in Clark County
Gypsum outcrop in Clark County.


Gypsum is an evaporite because it precipitates (settles) out of water as the water evaporates. the three varieties of gypsum are selenite, satin spar, and rock gypsum. Selenite, found throughout the Red Hills, has flat, diamond-shaped crystals that can be split into thin sheets. Satin spar is white or pink and fibrous with a silky luster. Satin spar is found as thin layers in beds of rock gypsum and certain types of shale. Rock gypsum is common in Kansas. It occurs as thick beds, or layers, of sedimentary rock and is mined in the Red Hills of south-central Kansas and in northeastern Kansas.

Chemical compound: calcium sulfate containing water
Chemical formula: CaSO4•2H2O (Ca = calcium, S = sulfur, O = oxygen, H = hydrogen)
Color: often colorless, white, or gray
Specific gravity: 2.32
Luster: glassy to pearly
Hardness: 2
Amount of transparency: transparent to opaque


Buchanan, R., 2010, Kansas Geology: An Introduction to Landscapes, Rocks, Minerals, and Fossils (2nd ed.): Lawrence, Kansas, University Press of Kansas, 240 p.

Buchanan, R., and McCauley, J. R., 2010, Roadside Kansas: A Traveler's Guide to Its Geology and Landmarks (2nd ed.): Lawrence, Kansas, University Press of Kansas, 392 p.

Kansas Rocks and Minerals, Kansas Geological Survey Educational Series 2