metamorphic

Greenstone (likely serpentinite)

Serpentinite, chiefly serpentine-group minerals (Mg₃Si₂O₅(OH)₄), possibly with chlorite or magnetite

AI-generated identification · may be incorrect

Dark olive-green, massive, fine-grained, and weakly waxy to dull luster; hardness about 2.5–4 Mohs, with poor or absent cleavage and a typical specific gravity near 2.5–2.6. The rounded surface and subtle veining suggest a water-worn pebble.

Identified September 3, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when ultramafic mantle rocks such as peridotite are hydrated during hydrothermal alteration, commonly along tectonic plate boundaries and suture zones. Serpentinite can form from Precambrian to modern geological settings; age cannot be determined from the photograph.

Uses & applications

Used as decorative building stone, carving material, aggregate, and occasionally as a lapidary stone. Attractive polished pieces are collected, though fibrous asbestos-bearing varieties require care and should not be cut or abraded without testing.

Geological facts

The green color comes mainly from serpentine minerals, while dark specks may represent magnetite or chromite. Similar-looking greenstones can also be chlorite-rich metamorphic rock or altered basalt.

Field identification & locations

Field clues include low hardness, smooth waxy feel, green-black mottling, and possible white veins; a steel knife may scratch it. Common sources include California, Oregon, Washington, Italy, New Zealand, and the Alps.