Among the softest and most useful of minerals

Gypsum is actually a group of similar minerals with the chemical formula CaSO4·2H2O. Two varieties are the fibrous satin spar (seen here) and selenite, which forms transparent sheets. Gypsum is number 2 on the Mohs hardness scale. It is an evaporite mineral, which means that it forms by deposition out of water solution in lakes and marine basins. It can be found worldwide and has a large number of industrial uses, including plaster of Paris and gypsum wallboard (“drywall”).

The specimen in this exhibit is from the collection of the late Dr. Kenneth Ohme of Mitchell, Nebraska. Look for gypsum in other exhibits in the museum.