metamorphic

Rounded greenstone cobble

Likely altered basalt/greenstone; commonly chlorite–actinolite–epidote rich

AI-generated identification · may be incorrect

Fine-grained, dull to faintly waxy luster, olive-green to gray-green, with no visible crystals or cleavage; estimated Mohs hardness 5–6 and specific gravity about 2.8–3.2. The smooth oval shape reflects water abrasion rather than crystal form.

Identified September 21, 2026More metamorphic →

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Physical properties

Formation & geological history

Probably metamorphosed or hydrothermally altered basalt, formed during ancient oceanic volcanism and later recrystallized under low-grade metamorphic conditions. Its exact geological age cannot be determined from the image.

Uses & applications

Used mainly as a decorative or teaching specimen, landscaping stone, and occasionally for carving or polished stone objects; it has little gem value unless unusually attractive or locally significant.

Geological facts

“Greenstone” is a field term rather than one precise mineral or rock; its color commonly comes from chlorite, actinolite, epidote, or serpentine. A streak, hardness, density, and thin-section test would be needed for confident identification.

Field identification & locations

Common as rounded river, beach, and glacial cobbles in regions containing altered volcanic rocks, including the Pacific Northwest, New England, Scotland, and New Zealand. Look for green fine grain, heavy density, and inability to scratch with a steel knife; avoid confusing it with serpentine or weathered basalt.