mineral

Prehnite

Prehnite - Ca2Al(AlSi3O10)(OH)2

Hardness: 6-6.5 (Mohs), Color: Pale green to yellow-green (often semi-translucent), Luster: Vitreous to pearly, Crystal Structure: Orthorhombic (often occurs in botryoidal or globular masses), Cleavage: Distinct in one direction, Specific Gravity: 2.80–2.90

Hardness: 6-6

Identified March 21, 2026More mineral →

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Physical properties

Formation & geological history

Formed as a secondary or hydrothermal mineral in cavities of mafic volcanic rocks (like basalt). It typically forms at low temperatures in igneous environments and occasionally in low-grade metamorphic rocks.

Uses & applications

Used primarily as a gemstone for jewelry (beads, cabochons) and as a highly sought-after mineral specimen for collectors.

Geological facts

Prehnite was the first mineral to be named after a person (Colonel Hendrik Von Prehn) in 1788. It is sometimes called 'Cape Chrysolite' when found in South Africa.

Field identification & locations

Identify by its distinct 'milky' or translucent apple-green color and its common occurrence in round, grape-like clusters (botryoidal). In the field, look for it in volcanic gas bubbles (amygdules). Found in South Africa, Australia, and the USA (New Jersey).