Chemical Formula: CaSO4 x 2H2O
Color: Colorless, white, beige, or brown
Importance: Major use is in drywall, plaster, and cement. Can also be added to fertilizers. Certain varieties, namely Satin Spar and Alabaster, are used for ornamental purposes.
Other Interesting Information: One of the more common minerals on Earth. Is found in large quantities in many localities. Very similar to anhydrite (CaSO4), with the only difference being gypsum has water in its chemical formula.
My Take: Gypsum is very special due to the fact that it can form in almost any shape. Satin Spar forms in fibers, Selenite in tabs and layers, and Alabaster in very fine grains. Also comes in many varieties, which most other minerals don’t do.
For More Information: http://www.minerals.net/mineral/gypsum.aspx