igneous
Polished dark stone, likely basalt or gabbro
Fine-grained mafic igneous rock; identification is uncertain from the image alone
AI-generated identification · may be incorrectDark gray-green, rounded and glossy from polishing or wetness, with faint lighter mineral flecks; likely Mohs hardness 5–6, opaque, with no visible cleavage and granular crystalline texture. The surrounding slab appears to be a separate light-colored granite.
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Physical properties
Dark gray-green, rounded and glossy from polishing or wetness, with faint lighter mineral flecks; likely Mohs hardness 5–6, opaque, with no visible cleavage and granular crystalline texture. The surrounding slab appears to be a separate light-colored granite.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface; gabbro is its coarse-grained underground equivalent. These rocks range from Precambrian to modern in age and occur in volcanic terrains and oceanic crust.
Uses & applications
Commonly used as aggregate, road stone, building stone, landscaping material, and occasionally as a tumbled or polished decorative specimen. This small piece has modest commercial value.
Geological facts
Basalt is rich in pyroxene and plagioclase, commonly with olivine or magnetite; gabbro has the same chemistry but larger crystals. The exact identity would require examining grain size, streak, magnetism, or a fresh surface.
Field identification & locations
Test for weak magnetism, inspect a fresh chip for interlocking dark crystals, and use a hardness test: it should scratch glass weakly or inconsistently. Common sources include India, Iceland, Hawaii, the Pacific Northwest, and many continental volcanic regions.
