Scientific Name: Calcium sulfate hydrate

Group: Sulfates

Chemical composition: CaSO4.2H2O

Colors: Colorless, white, light brown, yellow, pink

Hardness: 2

Formation: Monoclinic crystal; prismatic to tabular form

Principal Sources: Worldwide

Special Notes: The Romans discovered that heating gypsum to 600 degrees F made a plaster that sets hard when mixed with water. This plaster was used for building and is still widely used today.