igneous
Dark tumbled stone, likely basalt
Basalt; predominantly plagioclase feldspar, pyroxene, and possibly olivine
AI-generated identification · may be incorrectFine-grained, dark gray to black, with a dull to faintly vitreous luster; hardness about 6 Mohs, no visible cleavage, and typically dense (specific gravity ~2.8–3.0). The rounded shape suggests natural abrasion or tumbling, but the image is insufficient for definitive identification.
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Physical properties
Fine-grained, dark gray to black, with a dull to faintly vitreous luster; hardness about 6 Mohs, no visible cleavage, and typically dense (specific gravity ~2.8–3.0). The rounded shape suggests natural abrasion or tumbling, but the image is insufficient for definitive identification.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava rapidly cools at or near Earth’s surface, commonly in volcanic fields and oceanic crust. Individual specimens may range from recent volcanic material to billions of years old.
Uses & applications
Used as crushed aggregate, road stone, riprap, and occasionally as a decorative or lapidary material; ordinary pieces have little jewelry value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly forms extensive lava flows and ocean-floor crust.
Field identification & locations
Look for a uniformly fine texture, dark color, high density, and resistance to scratching; a streak test, magnetism test, and fresh interior would help distinguish basalt from slag or dark minerals. Common worldwide, especially volcanic regions.
