sedimentary
Gypsum (Wallboard/Drywall)
Calcium Sulfate Dihydrate (CaSO4·2H2O)
Hardness: 2 (Mohs scale); Color: Typically white, gray, or colorless; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect; Specific gravity: 2.3
- Hardness
- 2 (Mohs scale)
- Color
- Typically white, gray, or colorless
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 2 (Mohs scale); Color: Typically white, gray, or colorless; Luster: Vitreous to pearly; Crystal structure: Monoclinic; Cleavage: Perfect; Specific gravity: 2.3
Formation & geological history
Formed as an evaporite mineral in saline marine basins. The gypsum in this image is processed into wallboard, a construction material that has been the standard for interior walls since the mid-20th century.
Uses & applications
Primary component of drywall (sheetrock) used in residential and commercial construction. Also used as a soil conditioner in agriculture and as a setting retarder in Portland cement.
Geological facts
Gypsum is the most common sulfate mineral and is massive enough to form large desert crystals known as 'Desert Roses'. In its industrial form within walls, it provides inherent fire resistance due to the water molecules trapped in its crystal structure.
Field identification & locations
In a domestic setting, it is identified by the smooth, painted surfaces of the walls. In the field, look for soft, crystalline masses that can be scratched by a fingernail. It is found globally in large sedimentary deposits such as those in the Michigan Basin or the Paris Basin.
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