igneous
Dark gray fine-grained stone, likely basalt
Basalt; chiefly plagioclase feldspar and pyroxene, commonly with minor olivine and iron oxides
AI-generated identification · may be incorrectTypically 5–6 Mohs, dark gray to black, fine-grained and generally nonfoliated, with dull to weakly vitreous luster. The specimen appears massive and fine-grained, though the image alone cannot confirm its mineral content or exact identity.
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Physical properties
Typically 5–6 Mohs, dark gray to black, fine-grained and generally nonfoliated, with dull to weakly vitreous luster. The specimen appears massive and fine-grained, though the image alone cannot confirm its mineral content or exact identity.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface, producing tiny crystals; most examples are Cenozoic to modern, though basalt occurs throughout geologic time. It commonly forms volcanic flows, oceanic crust, and dikes.
Uses & applications
Used as crushed aggregate, roadstone, railway ballast, building stone, and occasionally polished architectural material; ordinary pieces have little jewelry value.
Geological facts
The gray, compact appearance and apparent lack of visible crystals are consistent with basalt, but fine-grained dark andesite or a metamorphic rock such as hornfels are alternatives.
Field identification & locations
Look for a dense dark color, fine texture, hardness sufficient to scratch glass, and absence of layering or foliation; a streak test, magnetism, acid reaction, and thin-section or XRF analysis would improve identification. Common worldwide, especially volcanic regions and oceanic settings.
