It is a mineral with very low hardness, as it can be scratched with one´s nail. Usually translucent, there are transparent (selenite) and opaque varieties, forming beautiful prismatic and round tabular crystals (desert rose - formed in desertic plains from rare rain water evaporation).
Gypsum, Willow Creek Alberta, Canada
Gypsum can form more than 10-meter long crystals. It was found in a cave in Mexico. It is the most common sulphate in earth´s crust, and it is usually formed in marine evaporation lagoons (evaporites).
Gypsum is used especially in plaster manufacturing, but is also used as fertilizer. A finely grained massive variety (alabaster) is used in sculpture manufacturing.
Source: MM Gerdau - Museu das Minas e do Metal -