mineral
Prehnite
Ca2Al2Si3O10(OH)2
Hardness: 6-6.5 (Mohs scale); Color: Pale green to yellow-green, translucent to semi-transparent; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Cleavage: Good in one direction; Specific Gravity: 2.80-2.95.
- Hardness
- 6-6
- Color
- Pale green to yellow-green, translucent to semi-transparent
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-6.5 (Mohs scale); Color: Pale green to yellow-green, translucent to semi-transparent; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Cleavage: Good in one direction; Specific Gravity: 2.80-2.95.
Formation & geological history
Commonly formed in the cavities of mafic volcanic rocks (basalt). It is a secondary or hydrothermal mineral resulting from low-grade metamorphism or hydrothermal alteration of plagioclase feldspars.
Uses & applications
Primarily used as a gemstone for jewelry (cabochons and beads) and as a collector's mineral specimen.
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' due to its color.
Field identification & locations
Look for the characteristic 'grape-like' (botryoidal) clusters and the unique 'inner glow' or oil-like translucency. Common locations include South Africa, Australia, Scotland, and the USA (New Jersey and Virginia).
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Mineral
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