mineral

Prehnite

Prehnite (Ca2Al(AlSi3O10)(OH)2)

Hardness: 6-6.5 (Mohs scale); Color: Pale green to yellow-green; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Cleavage: Distinct in one direction; Specific gravity: 2.80 - 2.95.

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

Identified June 21, 2026More mineral →

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Physical properties

Hardness: 6-6.5 (Mohs scale); Color: Pale green to yellow-green; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Cleavage: Distinct in one direction; Specific gravity: 2.80 - 2.95.

Formation & geological history

Formed as a secondary or hydrothermal mineral in cavities of mafic volcanic rocks (like basalt). It typically occurs in low-grade metamorphic environments and is often associated with zeolites.

Uses & applications

Primarily used as a semi-precious gemstone in jewelry (cabochons and beads) and as a collector's specimen. It was once relatively rare but is now popular in the 'healing crystals' market.

Geological facts

Prehnite 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 'Grape Jade' when it occurs in botryoidal (grape-like) clusters.

Field identification & locations

Identify by its translucent 'velvety' or pearly green appearance and its tendency to have dark inclusions of epidote. Commonly found in South Africa, Australia, and the USA (New Jersey). Collectors should look for its distinct globular or radiating crystal habits.