Florida Geological Survey - Geology Topics
Identification: The mineral gypsum is a
hydrous calcium sulfate, CaSO4.2H2O.
It may be transparent to translucent when pure, but is often
colored gray, yellow, red, brown or black by impurities.
Gypsum has a white streak, is soft enough to be scratched by
a fingernail (hardness of 2.0), and has a low specific
gravity (2.2 to 2.4). Gypsum occurs in several forms, two of
which are known to occur in the State. Selenite is a
coarsely crystalline, transparent variety composed of flat,
angular crystals that can be easily split apart.
Massive gypsum is a granular variety, showing no crystal
Occurrence: No commercial deposits are known
to exist near the surface in Florida, though deposits of
commercial extent are believed to be present at
approximately 2,000 feet below the ground surface in Monroe
Use: When gypsum is heated and the water
within it driven off, it forms a Plaster of Paris, which has
the property of becoming hard after being mixed with water.