Gypsum
Chemical Formula	CaSO4·2H2O
Species	Sulfates
Crystal System	Monoclinic
Mohs Scale	2
Specific Gravity	2.31-2.33
Color	Colorless to white; may be yellow, tan, blue, pink, brown, reddish brown or gray due to impurities
Streak	White
Luster	Vitreous, Sub-Vitreous, Silky, Pearly, Dull
Refractive Index	n = 1.519 - 1.521 n = 1.522 - 1.523 n = 1.529 - 1.530
Diaphaneity	Transparent, Translucent, Opaque
Cleavage	PerfectPerfect and easy on , almost micaceous in some samples; on distinct, yielding a surface with a conchoidal fracture; on , yielding a fibrous fracture .
Fracture	Splintery, Conchoidal
Crystal Habit：Massive, flat. Elongated and generally prismatic crystals
Geological Setting：Commonest of the sulphate minerals, gypsum is found in marine evaporites, in caves where the air is dry enough to allow it to be deposited and remain, at fumaroles, and in the oxidized zones of sulfide deposits on occasion.