igneous
Likely weathered basalt or andesite fragment
Fine-grained volcanic rock, likely basaltic-andesite; exact identification requires testing
AI-generated identification · may be incorrectDark gray-brown, fine-grained, uneven and partly glassy/wet-looking surface with possible pale feldspar or alteration patches; typically hardness ~5–6, dull to weakly vitreous luster, no obvious cleavage, and specific gravity about 2.7–3.0.
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Physical properties
Dark gray-brown, fine-grained, uneven and partly glassy/wet-looking surface with possible pale feldspar or alteration patches; typically hardness ~5–6, dull to weakly vitreous luster, no obvious cleavage, and specific gravity about 2.7–3.0.
Formation & geological history
Formed when lava cooled rapidly at or near Earth’s surface, likely during a relatively recent volcanic episode; the visible weathering and alteration may have developed much later through groundwater exposure.
Uses & applications
Common basalt and andesite are used as crushed aggregate, road stone, riprap, and building stone; an unattractive fragment has little jewelry or commercial value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly forms oceanic crust and lava flows. The image alone cannot reliably distinguish basalt from andesite or altered volcanic rock.
Field identification & locations
Look for a dense, fine-grained texture, dark color, lack of visible large crystals, and resistance to scratching; a streak, magnetism test, fresh broken surface, and thin-section analysis would improve identification. Common worldwide, especially volcanic regions and oceanic terrains.
