mineral

Prehnite on Basalt

Prehnite - Ca2Al(AlSi3O10)(OH)2

Hardness: 6-6.5 (Mohs), Color: Pale green to yellowish-green or white, Luster: Vitreous to pearly, Crystal Structure: Orthorhombic, Cleavage: Good in one direction, Specific Gravity: 2.80-2.90

Hardness: 6-6

Identified February 22, 2026More mineral →

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Physical properties

Hardness: 6-6.5 (Mohs), Color: Pale green to yellowish-green or white, 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 (vugs) and fractures of mafic volcanic rocks like basalt. Typical of low-grade metamorphism or hydrothermal activity in igneous rocks.

Uses & applications

Used primarily as a semi-precious gemstone for jewelry (cabochons), as decorative architectural stone, and as a popular collector's mineral specimen.

Geological facts

Prehnite was the first mineral to be named after a person (Colonel Hendrik Von Prehn) in 1788. It is sometimes referred to as 'Grape Jade' when it forms in botryoidal, rounded clusters.

Field identification & locations

Identified in the field by its distinctive pale 'sea-foam' green color, brittle tenacity, and occurrence within bubble-like cavities in dark volcanic rock. Commonly found in New Jersey (USA), South Africa, Scotland, and Australia.

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