igneous
Polished dark stone, likely basalt or black jasper
Basalt (fine-grained plagioclase–pyroxene rock), possibly iron-rich jasper/chert
AI-generated identification · may be incorrectSmall, rounded and polished; dark blue-black with irregular pale gray-tan patches and subdued vitreous to waxy luster. Basalt has Mohs hardness about 6, no visible cleavage, fine crystalline texture, and specific gravity about 2.8–3.0; exact identification requires testing.
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Physical properties
Small, rounded and polished; dark blue-black with irregular pale gray-tan patches and subdued vitreous to waxy luster. Basalt has Mohs hardness about 6, no visible cleavage, fine crystalline texture, and specific gravity about 2.8–3.0; exact identification requires testing.
Formation & geological history
If basalt, it formed from rapidly cooled mafic lava, commonly in volcanic fields and oceanic crust, generally any age. If jasper/chert, it formed by silica-rich chemical or biogenic sediment accumulation and later silicification.
Uses & applications
Suitable as a tumbled stone, cabochon, paperweight, or decorative aggregate; basalt is widely used for crushed stone and construction, while jasper is used in ornamental jewelry.
Geological facts
The image alone cannot reliably distinguish polished basalt from black jasper, chert, or another dark decorative stone. A streak, hardness, density, and magnified texture test would improve identification.
Field identification & locations
Look for tiny interlocking crystals and weak magnetism in basalt; jasper/chert is usually more uniformly opaque, glassy or waxy, and scratches glass. Common sources include volcanic regions worldwide and silica-rich sedimentary formations.
