Basalt with Epidote (Greenstone)

Physical Properties

Hardness: 6-7 on Mohs scale. Color: Dark grey to black matrix with characteristic pistachio-green or forest-green inclusions. Luster: Dull to sub-vitreous. Structure: Fine-grained (aphanitic) or porphyritic with small visible crystals.

Formation & Geological History

Formed through low-grade hydrothermal metamorphism (Greenschist facies) of mafic volcanic rocks (basalt). Common in areas with ancient oceanic crust or subduction zones.

Uses & Applications

Used in crushed stone for construction, road base, and occasionally as decorative lapidary material for jewelry like cabochons.

Geological Facts

This material is often called 'Greenstone' by collectors. The green color comes from the alteration of primary minerals like pyroxene and plagioclase into chlorite and epidote.

Field Identification & Locations

Identify in the field by its high density and the presence of green patches or veins against a dark background. Commonly found in glacial drift or along volcanic coastlines.

Identified on: 4/22/2026

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