igneous
Likely tumbled dark volcanic rock
Probably basalt or fine-grained andesite; exact identification requires testing
AI-generated identification · may be incorrectDark gray-green, rounded and water-worn or tumbled, with a dull to faintly waxy luster and no visible crystals. Typical hardness is about Mohs 6, with specific gravity roughly 2.7–3.0; it appears massive and non-cleaved.
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Physical properties
Dark gray-green, rounded and water-worn or tumbled, with a dull to faintly waxy luster and no visible crystals. Typical hardness is about Mohs 6, with specific gravity roughly 2.7–3.0; it appears massive and non-cleaved.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in oceanic crust and volcanic fields. Its geological age may range from recent to billions of years; the smooth shape indicates abrasion or tumbling.
Uses & applications
Common basalt is used for aggregate, roadstone, riprap, and occasionally carving or decorative specimens; this small piece has minimal commercial value.
Geological facts
The slight greenish translucence at thinner edges could indicate altered basalt, and the gray-green appearance may also fit serpentinite or another dark rock. A photo alone cannot distinguish these reliably.
Field identification & locations
Look for fine grain, high density, and possible tiny vesicles or feldspar specks; it should not fizz strongly in dilute acid. A streak, hardness test, magnet test, and specific-gravity measurement would improve identification.
