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Smithsonian National Museum of Natural History


Photograph of gypsum needles (117513) from the National Mineral Collection
Photo by Chip Clark. Click to zoom.
Catalog Number NMNH 117513-00
Locality San Luis Potosí, Mexico

Gypsum is hydrated calcium sulfate and a relatively common mineral. It is used in construction as drywall and an ingredient in plaster and fertilizer. The name is derived from the Greek “gypsos” meaning “chalk or plaster.” Gypsum is typically colorless to white, but due to impurities it can occur in shades of yellow, blue, pink, brown or gray. It typically forms as flat, elongated prismatic crystals that are mostly transparent and often times twinned. This cluster of gypsum has clear needle-like crystals.


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