igneous
Blue-gray volcanic rock, likely basalt
Basalt; fine-grained mafic rock composed mainly of plagioclase and pyroxene, with possible alteration minerals
AI-generated identification · may be incorrectDark blue-gray, dull to weakly silky surface, fine-grained and rounded/weathered. Typical basalt hardness is about 5–6 Mohs, with no visible cleavage and specific gravity around 2.8–3.0; the blue tint may reflect surface alteration or lighting.
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Physical properties
Dark blue-gray, dull to weakly silky surface, fine-grained and rounded/weathered. Typical basalt hardness is about 5–6 Mohs, with no visible cleavage and specific gravity around 2.8–3.0; the blue tint may reflect surface alteration or lighting.
Formation & geological history
Basalt forms when low-silica lava rapidly cools at or near the surface, commonly in volcanic fields and fissure eruptions. The specimen may be relatively young, but its age cannot be determined from the photograph.
Uses & applications
Used as crushed aggregate, roadstone, building stone, and occasionally as a decorative material. This nondescript piece has little jewelry or collector value.
Geological facts
The reported location near 13.2°N, 39.2°E lies in Ethiopia’s volcanically active Afar–Tigray region, where basaltic lava flows are common. A blue-green appearance can also result from alteration to chlorite, epidote, or copper minerals.
Field identification & locations
Look for a very fine-grained texture, dark color, high density, and possible tiny vesicles or feldspar crystals. A streak, magnetism test, acid test, and close examination of a fresh broken surface would help distinguish basalt from altered volcanic rock or blue-gray slag.
