mineral
Prehnite
Prehnite, Ca2Al(AlSi3O10)(OH)2
AI-generated identification · may be incorrectHardness: 6-6.5 (Mohs scale), Color: Pale green to yellow-green, Luster: Vitreous to pearly, Crystal Structure: Orthorhombic (often occurs in botryoidal or globular habits), Cleavage: Distinct in one direction, Specific Gravity: 2.80 - 2.95
- Hardness
- 6-6
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Physical properties
Hardness: 6-6.5 (Mohs scale), Color: Pale green to yellow-green, Luster: Vitreous to pearly, Crystal Structure: Orthorhombic (often occurs in botryoidal or globular habits), Cleavage: Distinct in one direction, Specific Gravity: 2.80 - 2.95
Formation & geological history
Formed in low-grade metamorphic environments and hydrothermal veins, typically as a secondary mineral in the cavities of mafic volcanic rocks like basalt. Many specimens date from the Mesozoic era.
Uses & applications
Primarily used as a gemstone for jewelry (cabochons and beads) and as a popular collector's mineral specimen. Historically used for minor ornamental carvings.
Geological facts
It was the first mineral to be named after a person, Colonel Hendrik Von Prehn, who discovered it in South Africa in 1788. It is sometimes called 'Cape Emerald' although it is not an emerald.
Field identification & locations
Identify by its characteristic 'seafoam' green color, greasy luster, and common botryoidal (grape-like) formation. Found commonly in South Africa, Australia, and the United States (New Jersey/Connecticut). Collectors look for clarity and the presence of epidote inclusions.
