igneous
Dark mafic rock, possibly basalt or altered gabbro
Basaltic rock; commonly composed of plagioclase feldspar, pyroxene, and possibly olivine or iron oxides
AI-generated identification · may be incorrectAppears black to dark brown, fine- to medium-grained, with dull to weakly vitreous luster and irregular fracture; estimated Mohs hardness 5–6 and specific gravity about 2.8–3.2. The image is insufficient to confirm grain size, cleavage, or exact mineralogy.
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Physical properties
Appears black to dark brown, fine- to medium-grained, with dull to weakly vitreous luster and irregular fracture; estimated Mohs hardness 5–6 and specific gravity about 2.8–3.2. The image is insufficient to confirm grain size, cleavage, or exact mineralogy.
Formation & geological history
Likely formed from cooling mafic lava or shallow magma, generally in volcanic settings; age cannot be determined visually. Weathering may produce the brown surface and pale mineral patches.
Uses & applications
Used as aggregate, roadstone, riprap, and occasionally decorative stone; unexceptional pieces have little jewelry value.
Geological facts
Basalt is Earth’s most common volcanic rock and forms much of the oceanic crust. A metallic streak or strong magnetism could indicate abundant magnetite, while vesicles would support a volcanic origin.
Field identification & locations
Look for a very dark color, dense feel, tiny interlocking crystals, and possible weak magnetism; a fresh broken surface is more diagnostic than the weathered exterior. Common worldwide, especially volcanic regions and oceanic crust.
