igneous
Black polished stone, likely basalt
Basalt; fine-grained mafic volcanic rock composed mainly of plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to black, opaque, smooth polished surface, typically dull to subvitreous luster; hardness about 5–6 Mohs, very fine-grained, with no visible cleavage. The rounded shape indicates tumbling or water wear.
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Physical properties
Dark gray to black, opaque, smooth polished surface, typically dull to subvitreous luster; hardness about 5–6 Mohs, very fine-grained, with no visible cleavage. The rounded shape indicates tumbling or water wear.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly from volcanic eruptions and oceanic crust formation; specimens may range from recent to billions of years old.
Uses & applications
Used as aggregate, paving stone, riprap, and decorative stone; polished pieces are sold as worry stones, paperweights, or simple lapidary collectibles.
Geological facts
Its dark color reflects iron- and magnesium-rich minerals. Some visually similar polished pieces may instead be black chert, obsidian, or industrial slag, which cannot be distinguished confidently from this photograph alone.
Field identification & locations
Likely basalt if it feels relatively heavy, has tiny crystalline specks, and shows no conchoidal fracture; a streak test, magnification, and specific-gravity test would help. Common worldwide, especially volcanic regions and beaches.
