mineral

Prehnite

Prehnite (Ca2Al(AlSi3O10)(OH)2)

Hardness: 6-6.5 (Mohs); Color: Pale green to yellow-green; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Specific Gravity: 2.80-2.95

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

Identified May 29, 2026More mineral →

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Physical properties

Hardness: 6-6.5 (Mohs); Color: Pale green to yellow-green; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Specific Gravity: 2.80-2.95

Formation & geological history

A secondary mineral formed in cavities of mafic volcanic rocks (basalt) and sometimes in low-grade metamorphic rocks through hydrothermal processes. Often occurs with zeolites.

Uses & applications

Primarily used as a gemstone for jewelry (cabochons) and as a collector specimen. It is sometimes used in industrial applications as an indicator mineral for metamorphic facies.

Geological facts

Prehnite was the first mineral to be named after an individual (Colonel Hendrik von Prehn) in 1788. Large, high-quality specimens are relatively rare compared to other silicate minerals.

Field identification & locations

Identify by its distinct 'seafoam green' color and habit of forming botryoidal (grape-like) clusters in volcanic basalt cavities. Commonly found in South Africa, Australia, and New Jersey (USA).