igneous
Polished dark stone, likely basalt or fine-grained mafic rock
Basalt (approximately; commonly plagioclase, pyroxene, and minor olivine/magnetite)
AI-generated identification · may be incorrectDark gray to black, fine-grained, opaque, and dull to mildly vitreous; Mohs hardness about 5–6, with no visible cleavage and typical specific gravity around 2.8–3.0. The smooth surface indicates tumbling or polishing.
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Physical properties
Dark gray to black, fine-grained, opaque, and dull to mildly vitreous; Mohs hardness about 5–6, with no visible cleavage and typical specific gravity around 2.8–3.0. The smooth surface indicates tumbling or polishing.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust. Most examples are geologically young relative to continental rocks, ranging from recent eruptions to billions of years old.
Uses & applications
Used as aggregate, road stone, building stone, paving, and landscaping material; polished pieces are sold as inexpensive worry stones or curiosities.
Geological facts
The image does not show diagnostic crystals or textures, so exact identification is uncertain; it could also be another dark volcanic rock or a polished industrial stone.
Field identification & locations
Look for a uniformly fine texture, high density, black streak, and lack of fizz with dilute acid; a magnet may detect magnetite-rich basalt. Common worldwide, especially Hawaii, Iceland, India, and oceanic volcanic regions.
