Gypsum (Hydrous Calcium Sulfate)
The name gypsum comes from a Greek work meaning calcined or burned. Selenite, a variety of gypsum with colorless, clear crystals, gets its name from a Greek word for moon. This is because the pear-like luster of selenite gypsum resembles moonlight.
Although generally a common mineral, gypsum has very limited production in Ohio. In 1997, Ohio ranked 14th nationally out of a total of 18 producing states. During that year only one Ohio company (in Ottawa County) produced gypsum, with a yield of 264,154 tons having a value of approximately $2 1/3 million. Gypsum has many applications. Industrially, it is used in the production of cement, plaster-of-Paris, and as a component of plasterboard. Alabaster, another variety of gypsum, has many ornamental uses.
Anhydrite has the same chemical content as gypsum except for water. Gypsum contains water, anhydrite does not. In fact, anhydrite specimens that are exposed to moisture may absorb water, and be transformed into gypsum.
Gypsum is a very common mineral. It is found in many places, some of the more important being in Europe, Africa and North America. Gypsum occurs in massive form in northern Ohio, where it was mined until recently. Moderately large, well-formed crystals of clear selenite gypsum are found in northeastern Ohio in silts and clays deposited in beds of former glacial lakes.