igneous
Tumbled gray stone, likely serpentinite or weathered basalt
Tentatively serpentinite (predominantly serpentine-group minerals); identification is uncertain from the photograph
AI-generated identification · may be incorrectDark gray-green, rounded, fine-grained, and dull to slightly waxy with pale veins or patches; likely Mohs 3–6 depending on composition, with no visible crystal faces or cleavage. The smooth surface indicates natural water wear or tumbling.
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Physical properties
Dark gray-green, rounded, fine-grained, and dull to slightly waxy with pale veins or patches; likely Mohs 3–6 depending on composition, with no visible crystal faces or cleavage. The smooth surface indicates natural water wear or tumbling.
Formation & geological history
If serpentinite, it formed by hydration and alteration of ultramafic mantle rock, commonly during oceanic crust formation and later tectonic uplift; if basalt, it formed from rapidly cooled lava. Geological age cannot be determined visually.
Uses & applications
Suitable mainly as a decorative or educational specimen; serpentinite is also used locally for carved objects and dimension stone, while basalt is used widely as aggregate and building stone.
Geological facts
Serpentinite commonly shows green-black mottling, slick or waxy surfaces, and white veins of magnesite or calcite. A hardness test and streak, acid, or mineralogical analysis would distinguish it from basalt and other dark stones.
Field identification & locations
Common in ophiolite belts and ultramafic terrains; basalt is widespread in volcanic regions. Check hardness, streak, magnetism, and reaction to dilute acid, but avoid destructive testing if collectible.
