mineral

Prehnite

Ca2Al(AlSi3O10)(OH)2

Hardness: 6-6.5; Color: Pale green to yellow-green, often translucent; Luster: Vitreous to pearly; Crystal System: Orthorhombic; Cleavage: Good in one direction. Often found in botryoidal or globular habits.

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

Identified July 9, 2026More mineral →

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Physical properties

Formation & geological history

Typically a secondary mineral occurring in cavities and veins of mafic volcanic rocks (basalt). It forms from low-grade metamorphic processes or hydrothermal alteration of plagioclase feldspars.

Uses & applications

Used primarily as a gemstone for jewelry (cabochons and beads) and as a collector specimen. It is also an indicator mineral for prehnite-pumpellyite facies metamorphism.

Geological facts

Named after Colonel Hendrik Von Prehn, who discovered it in 1774 at the Cape of Good Hope; it was the first mineral named after a person. Some specimens exhibit a glowing or 'moonstone-like' effect due to their fibrous structure.

Field identification & locations

Identify by its characteristic 'sea-foam' green color and translucent, pearly appearance. In the field, look for it in volcanic basalt bubbles (amygdules). Common locations include South Africa, Australia, and the USA (New Jersey).