mineral

Epidote

Epidote {Ca2}{Al2Fe3+}(Si2O7)(SiO4)O(OH)

Hardness: 6-7 (Mohs scale), Color: Pistachio-green to yellow-green or brownish-black, Luster: Vitreous to resinous, Crystal Structure: Monoclinic, Cleavage: Perfect in one direction, Specific Gravity: 3.3-3.6

Identified June 28, 2026More mineral →

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Physical properties

Formation & geological history

Formed during low-to-medium grade regional metamorphism of calcium-rich rocks like basalt, gabbro, or limestone. It often occurs in hydrothermal veins and vugs in igneous and metamorphic rocks.

Uses & applications

Primarily of interest to collectors and geologists; occasionally used as a minor gemstone (cabochons) when found in large, transparent crystals, or as a decorative stone (Unakite).

Geological facts

The name comes from the Greek word 'epidosis' meaning 'addition', referring to the crystal's base being longer on one side. It is a key index mineral for the greenschist metamorphic facies.

Field identification & locations

Identify in the field by its characteristic 'pistachio' green color and prismatic crystal habit. Commonly found in alpine veins, contact metamorphic zones, and altered volcanic rocks. Found globally in locations like Austria, Norway, and the USA.