metamorphic

Weathered greenstone

Metabasalt (greenstone), likely chlorite–actinolite–epidote rock

AI-generated identification · may be incorrect

Fine-grained, massive, rounded cobble with dull green-gray color, pale veins or alteration patches, and a waxy to dull luster. Typical hardness is about 5–6 Mohs; cleavage is absent to weak, and specific gravity is roughly 2.8–3.1.

Identified September 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when basaltic lava or gabbro was metamorphosed under low- to medium-grade conditions, commonly producing chlorite, actinolite, and epidote; its rounded shape reflects prolonged stream or beach transport. Exact geological age cannot be determined from the photograph.

Uses & applications

Used locally as durable aggregate, riprap, landscaping stone, and polished decorative material; attractive pieces may be collected but are generally low value.

Geological facts

The green color commonly results from iron- and magnesium-rich minerals formed during alteration or metamorphism. Pale patches may be quartz, feldspar, epidote, or weathering products.

Field identification & locations

Identify by its dense green-gray appearance, fine texture, toughness, and lack of visible sand grains or large crystals; a streak, hardness, and thin-section test would distinguish it from serpentinite or green volcanic rock. Common in metamorphic belts and glacial or stream gravels worldwide.