A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 6000 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.

The sulfate minerals all have one or more sulfate anions (SO4 -2).

Gypsum is a moderately common hydrous calcium sulfate mineral (CaSO4·2H2O). Gypsum has a nonmetallic luster, is usually clearish to whitish, is soft (H≡2), and rather fragile/brittle. Gypsum has 3 cleavage planes, one of which is well developed (“one good cleavage), and the other two are not well developed (“two poor cleavages”). Broken gypsum specimens are frequently thin plates - the consequence of the one good cleavage plane. Unbroken crystals show monoclinic symmetry.

Gypsum has economic value as a mineral. It is the starting ingredient for making plaster and wallboard. Translucent rock gypsum ("alabaster") has been carved to make decorative objects.

The specimen seen here consists of grayish-brown bladed gypsum composed of tightly-packed fibers intergrown with sandy sediments.

Locality: unrecorded / undisclosed site (possibly from Mexico)

Photo gallery of gypsum: