mineral
Prehnite with Epidote inclusions
Ca2Al(AlSi3O10)(OH)2
Hardness: 6-6.5 on Mohs scale; Color: pale green to yellow-green; 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
- Luster
- vitreous to pearly
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Physical properties
Hardness: 6-6.5 on Mohs scale; Color: pale green to yellow-green; Luster: vitreous to pearly; Crystal structure: Orthorhombic; Cleavage: Good in one direction; Specific Gravity: 2.80 - 2.90.
Formation & geological history
Formed as a secondary or hydrothermal mineral in cavities of mafic volcanic rocks (basalts and volcanic tuffs). It is often found associated with zeolites and formed during low-grade metamorphism.
Uses & applications
Mostly used as a gemstone for jewelry (cabochons or beads), ornamental carvings, and as a popular specimen for mineral collectors.
Geological facts
Prehnite was the first mineral to be named after a person, Colonel Hendrik Von Prehn, who discovered it in South Africa in the late 18th century. It is often called 'Grape Jade' in the trade due to its botryoidal growth habit.
Field identification & locations
Identified by its specific 'oily' or pearly luster and distinctive pale green color, often containing dark needle-like inclusions of Epidote. Commonly found in South Africa, Australia, and the United States (New Jersey/Connecticut).
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Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Sandstone with Mineral Veining or Crust
Sedimentary Sandstone (mostly SiO2 with Fe2O3 tinting)
sedimentary
Schist
Schist
Metamorphic
Potassium Feldspar (Orthoclase)
Orthoclase (KAlSi3O8)
mineral
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic