metamorphic

Likely serpentinite with a polished dark-green serpentine pebble

Serpentinite; chiefly serpentine-group minerals (Mg₃Si₂O₅(OH)₄), commonly with magnetite and minor chromite/talc

AI-generated identification · may be incorrect

Identified September 19, 2026More metamorphic →

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At a glance

Common name: Likely serpentinite with a polished dark-green serpentine pebble
Scientific name: Serpentinite; chiefly serpentine-group minerals (Mg₃Si₂O₅(OH)₄), commonly with magnetite and minor chromite/talc
Category: metamorphic
Identified: September 19, 2026
Method: Standard

AI Estimated Value

$5-$25 for common pieces; $10-$60 for a polished pebble or attractive lapidary specimen.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

The broken slab is fine-grained, green-gray, subtly speckled, and weakly lustrous, consistent with serpentinite. Serpentine has Mohs hardness about 2.5–4, waxy to dull luster, and no consistent cleavage; specific gravity is roughly 2.5–2.7. The polished pebble appears dark green-black and may be serpentine, nephrite-like material, or another polished mafic stone; the image alone cannot separate these confidently.

Formation & geological history

Forms when ultramafic mantle rocks such as peridotite hydrate during low-temperature metamorphism, commonly along faults and subduction zones. The specimen is geologically plausible near 38.7°N, 121.3°W, where Sierra Nevada foothill ophiolitic and Coast Range-related serpentinite occur, generally Mesozoic in age.

Uses & applications

Used as decorative stone, carvings, lapidary material, and occasionally dimension stone; serpentinite has also been used historically for ornamental architecture. Avoid dust, as some serpentinite bodies may contain asbestos-form minerals.

Geological facts

A useful confirmation is a streak or hardness test: it is commonly scratched by a steel knife and may leave a pale greenish-white streak. Fresh surfaces can show a slick, waxy texture and black magnetite grains.

Field identification & locations

Commonly found in California mélange, ophiolite, and fault-zone exposures. Do not saw or grind unknown serpentinite dry; use wet methods and respiratory protection.