metamorphic

Green river-worn pebble, likely serpentinite

Serpentinite (serpentine-group minerals; identification is provisional from the photograph)

AI-generated identification · may be incorrect

Dark green to gray-green, smooth and rounded with mottled pale patches and a subdued, waxy-to-dull luster. Serpentine minerals have Mohs hardness about 2.5–5.5 and a platy/foliated crystal structure; exact composition and specific gravity cannot be determined visually.

Identified October 4, 2026More metamorphic →

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Physical properties

Formation & geological history

Serpentinite forms when ultramafic rocks are altered by water, commonly along tectonic plate boundaries; the pebble’s rounded shape suggests later transport by water. Its age cannot be inferred from the image.

Uses & applications

Serpentinite is used as decorative stone, carving material, and occasionally as a source of mineral specimens; this small pebble has little commercial use.

Geological facts

Serpentine is a mineral group, not a single mineral, and commonly gives serpentinite its green color.

Field identification & locations

Look for a smooth, waxy feel, green mottling, and softness; compare with a streak or hardness test, since many other rocks resemble it. Serpentinite occurs in metamorphic belts worldwide.