metamorphic

Greenstone pebble

Greenstone (metamorphosed mafic rock, commonly altered basalt); exact identification requires testing

AI-generated identification · may be incorrect

Rounded, fine-grained olive-green to gray pebble with a dull to slightly waxy sheen and dark patches. Greenstone is typically composed of chlorite, epidote, and actinolite; hardness is variable, commonly about 5–6, with no obvious cleavage and an interlocking crystalline texture.

Identified October 13, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when basalt or other mafic volcanic rock was altered by low-grade metamorphism and hydrothermal fluids. Such rocks occur in ancient and modern volcanic belts; the specimen’s age cannot be determined from the image.

Uses & applications

Greenstone is used locally as dimension stone, aggregate, and decorative material; attractive polished pieces are collected or made into jewelry.

Geological facts

“Greenstone” describes a broad range of green, altered mafic rocks rather than one precise mineral species.

Field identification & locations

Look for a dense, fine-grained green rock with chlorite/epidote-like color and commonly darker inclusions; confirm with hardness, streak, and mineral examination. Found in metamorphic belts worldwide.