metamorphic

Stream-worn greenstone (likely serpentinite or altered basalt)

Serpentinite, chiefly serpentine-group minerals; possibly chlorite–actinolite greenstone

AI-generated identification · may be incorrect

Dark green to gray-green, fine-grained, massive, and strongly water-polished with a dull to waxy luster; likely Mohs hardness 2.5–5.5, with little visible cleavage. The faint pale veining and mottled surface are consistent with serpentinization or low-grade metamorphic alteration.

Identified September 9, 2026More metamorphic →

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At a glance

Common name: Stream-worn greenstone (likely serpentinite or altered basalt)
Scientific name: Serpentinite, chiefly serpentine-group minerals; possibly chlorite–actinolite greenstone
Category: metamorphic
Identified: September 9, 2026
Method: Standard

AI Estimated Value

About $5–$30 as an ordinary stream-worn specimen; larger attractive polished pieces may sell for $30–$150.

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

Formed when ultramafic mantle rock, commonly peridotite, was hydrated and metamorphosed; comparable greenstones can form by alteration of basalt. The specimen’s age cannot be determined from an image; it was later rounded by stream transport.

Uses & applications

Usually collected as a natural specimen or used as decorative stone, carving material, aggregate, or locally as dimension stone; serpentinite is also an ornamental stone. It is not gem-quality based on this appearance.

Geological facts

The smooth shape and reflective surface are primarily caused by prolonged abrasion in flowing water, not by crystal growth. Serpentinite may contain trace chrysotile or other asbestos minerals, so avoid cutting, drilling, or generating dust until tested.

Field identification & locations

Identify by its green-black color, waxy feel, low-to-moderate hardness, dense texture, and lack of obvious grains; a streak, hardness, and mineral test would distinguish it from basalt or greenstone. Common in ophiolite belts and streams draining ultramafic or metamorphic terrain.