mineral

Prehnite

Prehnite - Ca2Al(AlSi3O10)(OH)2

Hardness: 6-6.5; Color: Pale green to yellow-green; Luster: Vitreous to pearly; Crystal structure: Orthorhombic (often occurs as botryoidal or globular masses); Specific Gravity: 2.80-2.95

Hardness: 6-6
Color: Pale green to yellow-green
Luster: Vitreous to pearly

Identified July 19, 2026More mineral →

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Physical properties

Hardness: 6-6.5; Color: Pale green to yellow-green; Luster: Vitreous to pearly; Crystal structure: Orthorhombic (often occurs as botryoidal or globular masses); Specific Gravity: 2.80-2.95

Formation & geological history

Formed primarily in the cavities and fractures of mafic volcanic rocks (basalt) through low-grade metamorphism or hydrothermal activity. Often found in association with zeolites.

Uses & applications

Used mostly as a gemstone for jewelry (beads, cabochons) and as a collector's mineral specimen. Some varieties show chatoyancy.

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 and origin.

Field identification & locations

Identified by its distinctive oily green color and botryoidal habit. Common locations include South Africa, Australia, and the United States (New Jersey). Collectors should look for internal crystalline structures which distinguish it from glass.