Mineral, Gypsum

Photo of a Gypsum sample, which is a mineral of calcium (CaSO4.2H2O / di-hydrated calcium sulphate). The name derives from the word "Γύψος", i.e. "cast" that included the old plaster, lime, anhydrite and other similar building materials.
Its fracture is splintery. It is flexible but not elastic. It has a specific gravity of 2.32 g/cm3. It crystallizes in monoclinic crystallographic system. It poses the number 2 in Mohs hardness scale (scratched with a fingernail). Its color varies from colorless, white, or gray and depending to its impurities can have various shades of yellow, red, brown. Luster is vitreous to pearly and silky, non-metallic. The streak is white.
It is a common mineral and it is found in sedimentary rocks. It is formed during the evaporation of sea water in closed basins or by hydration of anhydrite. It is located in clays, in clay schist and is accompanied by anhydride, halite, dolomite, calcite, sulfur, pyrite and quartz.