igneous
Dark gray stone, possibly basalt or andesite
Fine-grained mafic to intermediate volcanic rock; precise identification is limited by the cropped image
AI-generated identification · may be incorrectDark gray, dull to faintly waxy luster, massive and fine-grained with no obvious crystals or cleavage; likely Mohs hardness about 5–6 and specific gravity roughly 2.7–3.0.
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Physical properties
Dark gray, dull to faintly waxy luster, massive and fine-grained with no obvious crystals or cleavage; likely Mohs hardness about 5–6 and specific gravity roughly 2.7–3.0.
Formation & geological history
Likely cooled lava formed at or near Earth’s surface, generally younger than surrounding continental crust; distinguishing basalt from andesite requires texture, density, and mineral examination.
Uses & applications
Common equivalents are used as aggregate, road stone, riprap, and building stone; attractive polished pieces may be sold as inexpensive decorative or lapidary material.
Geological facts
Basalt is the most widespread volcanic rock on Earth and commonly contains microscopic plagioclase and pyroxene crystals, sometimes with olivine or magnetite.
Field identification & locations
Look for a dense, nonlayered dark rock with tiny interlocking crystals; a streak test, magnetism test, fresh fracture, and thin-section or chemical analysis can separate basalt, andesite, and other dark rocks. Common localities include volcanic regions worldwide.
