igneous
Polished black stone, likely basalt
Basalt; predominantly plagioclase feldspar and pyroxene, commonly with minor magnetite or olivine
AI-generated identification · may be incorrectTypically dark gray to black, fine-grained, opaque, and dull to subtly waxy; hardness about 5–6 Mohs, with no visible cleavage and irregular fracture. The smooth surface appears polished or naturally water-worn, so exact identification from the image alone is limited.
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Physical properties
Typically dark gray to black, fine-grained, opaque, and dull to subtly waxy; hardness about 5–6 Mohs, with no visible cleavage and irregular fracture. The smooth surface appears polished or naturally water-worn, so exact identification from the image alone is limited.
Formation & geological history
Basalt forms when low-viscosity mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust; specimens range from recent to Precambrian in age.
Uses & applications
Used as crushed aggregate, road base, concrete, riprap, paving, and decorative stone; polished pieces are sold as ornaments or worry stones.
Geological facts
Its dark color reflects abundant iron- and magnesium-rich minerals. A magnet may show weak attraction if magnetite is present.
Field identification & locations
Look for a uniformly fine texture, high density, dark streakless appearance, and possible tiny feldspar crystals; test hardness against glass and inspect for vesicles. Common worldwide, especially volcanic regions and river gravels.
