metamorphic

Serpentine-rich metamorphic cobble

Serpentinite, principally antigorite/lizardite Mg3Si2O5(OH)4, possibly with magnetite and minor carbonate

AI-generated identification · may be incorrect

Typically olive-green to yellow-green, mottled, waxy to greasy luster, and massive rather than visibly crystalline; Mohs hardness about 2.5–4, with poor cleavage and specific gravity near 2.5–2.6. The rounded, polished appearance indicates natural water wear or tumbling.

Identified September 15, 2026More metamorphic →

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At a glance

Common name: Serpentine-rich metamorphic cobble
Scientific name: Serpentinite, principally antigorite/lizardite Mg3Si2O5(OH)4, possibly with magnetite and minor carbonate
Category: metamorphic
Identified: September 15, 2026
Method: Standard

AI Estimated Value

About $5–$30 for a common cobble; $30–$150 or more for unusually patterned, polished, or well-provenanced specimens.

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

Formation & geological history

Forms when ultramafic mantle rocks such as peridotite are hydrated during hydrothermal alteration, commonly along faults and plate boundaries. Serpentinization is generally Paleozoic to modern, depending on the host terrane.

Uses & applications

Used as ornamental stone, carvings, countertops, and historically as a source of magnesium; attractive pieces are collected, though fibrous asbestos-bearing varieties require caution. It is not typically used as a gemstone unless polished.

Geological facts

The specimen’s green-gold coloration and smooth waxy surface are consistent with serpentinite, but an image cannot exclude weathered greenstone, nephrite, or altered basalt. Avoid cutting or sanding unknown serpentinite because some deposits contain chrysotile asbestos.

Field identification & locations

Field clues include a low hardness, greasy feel, green mottling, and possible magnetism from magnetite; it may occur in ophiolites and mountain belts. Common localities include California, Italy, New Zealand, Canada, and the Ural region.