metamorphic
Tumbled dark green beach pebble
Likely serpentinite or altered basalt; exact identification requires testing
AI-generated identification · may be incorrectFine-grained, smooth and rounded from wave abrasion; olive-green to brown with a waxy-to-dull luster. Likely hardness about 3–6 Mohs depending on composition, with no visible cleavage or crystals.
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Physical properties
Fine-grained, smooth and rounded from wave abrasion; olive-green to brown with a waxy-to-dull luster. Likely hardness about 3–6 Mohs depending on composition, with no visible cleavage or crystals.
Formation & geological history
Probably a glacially transported or locally eroded mafic/ultramafic rock, later naturally polished by coastal abrasion. Its precise geological age and formation cannot be determined from the image.
Uses & applications
Primarily a collectible beach stone, lapidary rough, or decorative pebble; if serpentinite, similar material is used for carvings, countertops, and ornamental stone. Typical value is low unless unusually attractive or from a notable locality.
Geological facts
The subdued green color may result from serpentine minerals, chlorite, epidote, or weathered ferromagnesian minerals. Surface color alone cannot reliably distinguish serpentinite from basalt, greenstone, or other dark metamorphic rocks.
Field identification & locations
Check streak, hardness, density, and reaction to dilute hydrochloric acid; serpentinite is often relatively soft and waxy, while basalt is harder and denser. Common possibilities occur in coastal areas and glacial deposits worldwide.
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