igneous
Polished black stone, likely basalt or black jasper
Basalt (fine-grained mafic volcanic rock), possibly dark microcrystalline silica (black jasper)
AI-generated identification · may be incorrectAppears black, opaque, and highly polished with subtle granular or reflective texture. Basalt has Mohs hardness about 6, dull-to-waxy luster, fine interlocking crystals, and no visible cleavage; jasper is harder (6.5–7) and waxier.
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Physical properties
Appears black, opaque, and highly polished with subtle granular or reflective texture. Basalt has Mohs hardness about 6, dull-to-waxy luster, fine interlocking crystals, and no visible cleavage; jasper is harder (6.5–7) and waxier.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly from Cenozoic to modern volcanic activity. Black jasper forms when silica-rich fluids replace or cement volcanic material.
Uses & applications
Used as a decorative stone, palm stone, cabochon, carving material, and occasionally aggregate or building stone. Value is generally modest unless the specimen has unusual patterning or provenance.
Geological facts
The elongated shape and glossy surface indicate tumbling or polishing rather than natural weathering. Exact identification requires a specific-gravity, streak, hardness, and preferably microscopic or chemical test.
Field identification & locations
Common in volcanic regions worldwide; black jasper occurs in silica-rich volcanic terrains. Basalt is typically slightly granular and may leave a gray streak, while jasper resists scratching by steel more strongly and may show conchoidal fracture.
