Properties
| Category | Sulfate minerals |
|---|---|
| Formula | CaSO4·2H2O |
| Crystal system | Monoclinic |
| Color | Colorless (in transmitted light) to white; often tinged other hues due to impurities; may be yellow, tan, blue, pink, dark brown, reddish brown or gray |
| Crystal habit | Massive, flat. Elongated and generally prismatic crystals |
| Cleavage | Perfect on {010}, distinct on {100} |
| Fracture | Conchoidal on {100}, splintery parallel to |
| Tenacity | Flexible, inelastic |
| Mohs scale hardness | 1.5–2 (defining mineral for 2) |
| Luster | Vitreous to silky, pearly, or waxy |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.31–2.33 |
From the Wikipedia article
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk chalk. Gypsum also crystallizes as translucent crystals of selenite. It forms as an evaporite mineral and as a hydration product of anhydrite. The Mohs scale of mineral hardness defines gypsum as hardness value 2 based on scratch hardness comparison.
Source
Source record: crystal-compendium/gypsum/minerals.json. Fetched from English Wikipedia by the operator 2 October 2026.
https://en.wikipedia.org/wiki/Gypsum — revision id 1375892327. Text and properties from Wikipedia, licensed CC BY-SA 4.0.