igneous
Tumbled basalt
Basalt; fine-grained mafic volcanic rock composed mainly of plagioclase and pyroxene, commonly with olivine
AI-generated identification · may be incorrectDark gray to black, rounded and polished, with a dull to weakly vitreous luster; typically hardness 5–6 Mohs, dense, fine-grained, and lacking visible cleavage or crystals.
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Physical properties
Dark gray to black, rounded and polished, with a dull to weakly vitreous luster; typically hardness 5–6 Mohs, dense, fine-grained, and lacking visible cleavage or crystals.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in oceanic crust, volcanic islands, and flood-basalt provinces. Most examples range from recent to hundreds of millions of years old; the image alone cannot establish age.
Uses & applications
Used as aggregate, road stone, riprap, paving, and sometimes landscaping material; tumbled pieces are sold for crafts, meditation, and mineral collections rather than jewelry.
Geological facts
Its dark color reflects abundant ferromagnesian minerals and relatively low silica. A small metallic-looking spot may be a vesicle, inclusion, or surface reflection, but the photograph is insufficient for certainty.
Field identification & locations
Common worldwide, including Hawaii, Iceland, India’s Deccan Traps, and oceanic crust. Field identification relies on dark color, high density, fine texture, and absence of visible quartz; a streak or hardness test can help distinguish it from slag or similar stones.
