mineral

Prehnite

Prehnite (Ca2Al2Si3O10(OH)2)

Hardness: 6 to 6.5 Mohs scale; Color: Pale green to yellow-green, semi-transparent to translucent; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Specific Gravity: 2.80 to 2.95.

Hardness: 6 to 6
Color: Pale green to yellow-green, semi-transparent to translucent
Luster: Vitreous to pearly

Identified July 8, 2026More mineral →

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Physical properties

Hardness: 6 to 6.5 Mohs scale; Color: Pale green to yellow-green, semi-transparent to translucent; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Specific Gravity: 2.80 to 2.95.

Formation & geological history

Formed as a secondary mineral in hydrothermal environments, typically in the cavities or veins of mafic volcanic rocks like basalt. Often associated with zeolites and formed at relatively low temperatures.

Uses & applications

Primarily used as a gemstone for jewelry (cabochons, beads) and as a collector's specimen. It was historically sometimes used as an ornamental stone.

Geological facts

It was the first mineral 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 characteristic pale 'apple-green' color and pearly luster. In the field, look for it in volcanic gas bubbles (vesicles). Significant deposits are found in Australia, South Africa, and the USA (New Jersey and Virginia).