Selenite
Image: Darla Sondrol (CC0)
Mineral NameSelenite
Chemical FormulaCaSO₄·2H₂O
Mohs Hardness1.5
Crystal Systemmonoclinic
Lustervitreous
Streak Colorwhite
Cleavageperfect on {010}, distinct on {100} and {111}
Fractureconchoidal
Specific Gravity2.32
Colorsclear, colorless, white, pale yellow, pale brown
Transparencytransparent
Type LocalityNot specified in metadata, but found worldwide (e.g., Naica, Mexico; Cave of the Crystals)
Mineral Groupsulfates
Usescollector, ornamental, sculpture, source of plaster of Paris
Associated Mineralshalite, anhydrite, sulfur, calcite, dolomite, clays, iron oxides
Raritycommon
Description
A clear, colorless to pale yellowish bladed crystal of gypsum, measuring 11 cm across. It exhibits excellent transparency and a vitreous luster, characteristic of the selenite variety.
Geological Context
Selenite forms as layers or crack fillings in sedimentary rocks, frequently associated with red beds. It also precipitates as bladed crystals in soils from groundwater.
