mineral
Polished black stone, likely black jasper or basalt
Microcrystalline quartz (SiO₂) if jasper; alternatively fine-grained basalt
AI-generated identification · may be incorrectOpaque black, smooth polished surface, subvitreous to dull luster, no visible crystals; jasper has Mohs hardness about 6.5–7, while basalt is about 5–6. Cleavage is absent; specific gravity is roughly 2.7–3.0.
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Physical properties
Opaque black, smooth polished surface, subvitreous to dull luster, no visible crystals; jasper has Mohs hardness about 6.5–7, while basalt is about 5–6. Cleavage is absent; specific gravity is roughly 2.7–3.0.
Formation & geological history
Black jasper forms when silica-rich fluids replace or cement volcanic sediments; basalt forms from rapidly cooled mafic lava, commonly in the Cenozoic to Precambrian geological record. The specimen appears shaped and polished, so its original texture is obscured.
Uses & applications
Used for cabochons, carvings, beads, worry stones, and ornamental objects; basalt is widely used as aggregate, paving stone, and construction material.
Geological facts
The image alone cannot reliably distinguish jasper from basalt or other black stones such as chert, obsidian, or slag. A streak, hardness, specific-gravity, and magnification test would improve identification.
Field identification & locations
Likely jasper if it resists scratching by steel and scratches glass; basalt is usually less glassy and may reveal tiny feldspar or pyroxene grains. Common sources include volcanic regions worldwide, especially India, Mexico, Australia, and the western United States.
