igneous
Polished black stone, likely basalt or black jasper
Basalt (fine-grained plagioclase–pyroxene rock) or microcrystalline quartz (black jasper); exact identification requires testing
AI-generated identification · may be incorrectOpaque black, smoothly polished, glassy to waxy luster, massive texture, and no visible crystals or cleavage. Basalt is typically Mohs 5–6 with specific gravity about 2.8–3.0; jasper is Mohs 6.5–7 and about 2.6.
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Physical properties
Opaque black, smoothly polished, glassy to waxy luster, massive texture, and no visible crystals or cleavage. Basalt is typically Mohs 5–6 with specific gravity about 2.8–3.0; jasper is Mohs 6.5–7 and about 2.6.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly from Cenozoic to present volcanic activity; jasper forms when silica-rich fluids replace or cement sediment, often in volcanic settings.
Uses & applications
Used as a decorative polished stone, worry stone, cabochon, carving material, or ornamental object; basalt is also widely used as aggregate and building stone.
Geological facts
The highly curved, glossy shape appears human-polished or tumbled rather than naturally weathered. A strong glassy translucence at thin edges would favor obsidian, while tiny crystalline grains and weak magnetism favor basalt.
Field identification & locations
Test inconspicuously: basalt may attract a strong magnet weakly, whereas jasper scratches glass and basalt usually does not; streak, hardness, and density can distinguish them. Common sources include volcanic regions worldwide, especially Mexico, India, China, and the western United States.
