mineral
Selenite (satin spar gypsum)
Gypsum, CaSO₄·2H₂O
AI-generated identification · may be incorrectTypically colorless to white or pale pink, with a pearly/silky luster and fibrous or bladed crystal structure; Mohs hardness 2, excellent one-direction cleavage, and specific gravity about 2.3. The fibrous striations and soft, easily scratched surface fit satin spar gypsum.
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Physical properties
Typically colorless to white or pale pink, with a pearly/silky luster and fibrous or bladed crystal structure; Mohs hardness 2, excellent one-direction cleavage, and specific gravity about 2.3. The fibrous striations and soft, easily scratched surface fit satin spar gypsum.
Formation & geological history
Forms when evaporating saline water deposits sulfate minerals in sedimentary evaporite beds, commonly from the Permian to Recent eras. Large crystals also grow in cavities and clay-rich deposits through groundwater evaporation.
Uses & applications
Used to make plaster, drywall, cement additives, and soil conditioners; attractive pieces are sold as inexpensive decorative or metaphysical specimens. It is too soft for most jewelry and scratches readily.
Geological facts
“Selenite” properly refers to clear crystalline gypsum, while fibrous varieties are called satin spar; trade names are often used loosely. It can be scratched with a fingernail and dissolves slowly in water.
Field identification & locations
Common in evaporite regions worldwide, notably Mexico, Morocco, Spain, the United States, and Australia. Confirm with a fingernail scratch, white streak, very low weight, and silky parallel fibers; avoid prolonged moisture and abrasion.
