Gypsum
Image: <a href="//commons.wikimedia.org/wiki/User:Archaeodontosaurus" title="User:Archaeodontosaurus">Didier Descouens</a> (CC BY-SA 4.0)
Mineral NameGypsum
Chemical FormulaCaSO4·2H2O
Mohs Hardness2
Crystal Systemmonoclinic
Lustervitreous
Streak Colorwhite
Cleavageperfect on {010}, good on {100}, distinct on {111}
Fractureconchoidal
Specific Gravity2.32
Colorswhite, colorless, pale yellow
Transparencytranslucent
Type LocalityArignac, Tarascon-sur-Ariège, Ariège, Midi-Pyrénées, France
Mineral GroupSulfates
Usesconstruction, plaster, fertilizer, sculpture, collector
Associated Mineralshalite, anhydrite, calcite, sulfur
Raritycommon
Description
This specimen features a large, translucent, colorless to pale white gypsum crystal exhibiting a classic swallowtail twin on {110}, with distinct striations and a vitreous luster.
Geological Context
Gypsum typically forms as an evaporite mineral in sedimentary environments, such as dried-up seas or saline lakes, where calcium sulfate precipitates from evaporating water. It can also form in hydrothermal veins or as a hydration product of anhydrite.
