Prehnite

Physical Properties

Hardness: 6-6.5 on Mohs scale; Color: Pale green to yellow-green; Luster: Vitreous to pearly; Crystal structure: Orthorhombic; Cleavage: Good in one direction; Specific gravity: 2.80-2.95.

Formation & Geological History

Formed in low-grade metamorphic conditions, typically in cavities and veins of mafic volcanic rocks (basalt). It is a secondary mineral resulting from the hydrothermal alteration of plagioclase feldspars.

Uses & Applications

Primarily used as a gemstone for jewelry (cabochons and beads) and as a decorative collector's specimen. It was also once used as a minor ore of aluminum in specific contexts.

Geological Facts

Prehnite was the first mineral to be named after a person (Colonel Hendrik von Prehn) in 1788. It often forms 'botryoidal' (grape-like) clusters and is frequently found associated with Zeolites.

Field Identification & Locations

Identify in the field by its distinct oil-green color, brittle tenacity, and appearance in volcanic gas bubbles (amygdules). Common locations include South Africa, Australia, and the United States (New Jersey/Virginia).

Identified on: 4/14/2026

Mode: Standard