metamorphic

Greenstone (likely metamorphosed basalt)

Metabasalt/greenstone; commonly composed of chlorite, actinolite, epidote, albite, and quartz

AI-generated identification · may be incorrect

Dark green-gray, fine- to medium-grained, mottled and weakly schistose with dull to slightly silky luster; hardness about 5–6 Mohs. The image suggests a tough, massive metamorphic rock rather than a discrete mineral crystal.

Identified September 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when basaltic oceanic crust was altered and metamorphosed by heat, pressure, and hydrothermal fluids, typically at greenschist-facies conditions during regional tectonism. Its exact geological age cannot be determined from the photograph.

Uses & applications

Used locally as crushed aggregate, riprap, landscaping stone, and occasionally decorative facing stone; attractive polished pieces may be collected but are generally low-value.

Geological facts

The term “greenstone” is a field/geologic description, not one precise mineral species; its green color usually comes from chlorite, actinolite, or epidote.

Field identification & locations

Identify by its dark green color, fine grain, compact toughness, and lack of obvious large crystals; a streak, hardness, thin-section, or laboratory test would distinguish it from serpentinite, amphibolite, or green volcanic rock. Common in metamorphic belts and altered ancient oceanic crust.