mineral
Prehnite
Ca2Al(AlSi3O10)(OH)2
Hardness: 6-6.5 on Mohs scale; Color: typically pale green to yellow-green; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Specific Gravity: 2.80-2.90.
- Hardness
- 6-6
- Color
- typically pale green to yellow-green
- Luster
- Vitreous to pearly
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Physical properties
Hardness: 6-6.5 on Mohs scale; Color: typically pale green to yellow-green; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Specific Gravity: 2.80-2.90.
Formation & geological history
Forms in cavities of mafic volcanic rocks (basalt) and occasionally in low-grade metamorphic zones. It is often a secondary mineral formed by hydrothermal activity.
Uses & applications
Primarily used as a gemstone for jewelry (cabochons and beads) and as a collector's mineral specimen. Some consider it an ornamental stone.
Geological facts
It was the first mineral named after a person, Colonel Hendrik Von Prehn, who discovered it in South Africa in 1788. It is also known for frequently containing dark green epidote inclusions.
Field identification & locations
Identify by its distinct 'sea-foam' green color and its tendency to form in globular or botryoidal (grape-like) clusters. Major deposits are found in South Africa, Australia, and the USA (New Jersey).
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Metamorphic
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
Nephrite Jade
Nephrite
Mineral/Rock
Granite
Granite (Phaneritic intrusive igneous rock)
igneous