mineral
Prehnite
Prehnite (Ca2Al(AlSi3O10)(OH)2)
Hardness: 6-6.5; Color: Pale green to yellow-green, translucent to semi-transparent; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Cleavage: Good in one direction; Specific gravity: 2.80-2.90.
- 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; Color: Pale green to yellow-green, translucent to semi-transparent; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Cleavage: Good in one direction; Specific gravity: 2.80-2.90.
Formation & geological history
Usually forms as a secondary or hydrothermal mineral in cavities (vugs) of mafic volcanic rocks like basalt. Formed during low-grade metamorphism.
Uses & applications
Used primarily as a gemstone for cabochons and beads, and as a popular mineral specimen for collectors.
Geological facts
Prehnite was the first mineral to be named after a person, Colonel Hendrik Von Prehn, who discovered it in 1788 at the Cape of Good Hope.
Field identification & locations
Identify by its 'grape-like' (botryoidal) habit, distinct yellowish-green color, and pearly luster. Common locations include South Africa, Australia, and the USA (New Jersey).
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