mineral

Prehnite

Prehnite - Ca2Al(AlSi3O10)(OH)2

Hardness: 6-6.5 (Mohs scale); Color: Pale green, light green, or yellowish-green; Luster: Vitreous to pearly; Crystal structure: Orthorhombic, typically appearing in botryoidal (grape-like) or globular masses; Cleavage: Good in one direction; Specific Gravity: 2.80 - 2.95.

Hardness: 6-6
Color: Pale green, light green, or yellowish-green
Luster: Vitreous to pearly

Identified March 23, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary mineral in cavities of mafic volcanic rocks (like basalt/diabase) and in low-grade metamorphic rocks. It often crystallizes from hydrothermal fluids during the cooling process of volcanic events.

Uses & applications

Commonly used as a semi-precious gemstone in jewelry (cabochons or faceted); widely sought after by mineral collectors for its unique habit and sea-foam green color.

Geological facts

Prehnite was the first mineral to be named after an individual, Colonel Hendrik Von Prehn, who discovered it in South Africa in 1788. It is sometimes nicknamed 'Cape Emerald'.

Field identification & locations

Identify in the field by its distinct pale 'sea-foam' green color and characteristic rounded, bubbly aggregates. Common locations include the Paterson area of New Jersey (USA), Mullane in South Africa, and the Kayes Region in Mali.