metamorphic

Serpentine-rich serpentinite pebble

Serpentinite; chiefly serpentine-group minerals (chrysotile, lizardite, antigorite), commonly with magnetite and relict olivine/pyroxene

AI-generated identification · may be incorrect

Typically dark green to olive, mottled, opaque, and waxy to dull with a smooth weathered surface; hardness about 2.5–4 Mohs, poor cleavage, fine-grained massive texture, and specific gravity roughly 2.5–2.7. The image suggests serpentinite, though exact identification requires hardness, streak, and mineral testing.

Identified September 17, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when ultramafic mantle rocks such as peridotite undergo hydration and low-temperature metamorphism, commonly in oceanic crust and tectonic belts. Most examples are Paleozoic to Cenozoic, but the specimen’s age cannot be determined visually.

Uses & applications

Used as decorative stone, carving material, aggregate, and historically as “green marble”; attractive pieces may be polished for jewelry or specimens.

Geological facts

Often contains magnetite and may be weakly magnetic; some serpentinite bodies contain asbestos-form serpentine minerals, so avoid cutting or generating dust.

Field identification & locations

Look for mottled green color, waxy feel, unusually low hardness, and association with dark ultramafic rocks; common in California, the Alps, New Zealand, and ophiolite belts worldwide. Value is typically $1–$15 for a common pebble, or $20–$100+ if unusually patterned and polished.