igneous
Dark tumbled stone, likely basalt
Basalt (fine-grained mafic volcanic rock; commonly plagioclase, pyroxene, and olivine)
AI-generated identification · may be incorrectHardness about 5–6 Mohs; dark gray to black, fine-grained, and generally dull to slightly glassy when polished. Typically massive with no visible cleavage and a specific gravity around 2.8–3.0.
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Physical properties
Hardness about 5–6 Mohs; dark gray to black, fine-grained, and generally dull to slightly glassy when polished. Typically massive with no visible cleavage and a specific gravity around 2.8–3.0.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, volcanic fields, and flood-basalt provinces. Its age may range from recent eruptions to billions of years.
Uses & applications
Used as aggregate, roadstone, building stone, and landscaping material; small polished pieces are sold as inexpensive worry stones or decorative specimens.
Geological facts
The photograph is low-resolution, so identification is approximate; the specimen could also be another dark volcanic rock such as andesite or a manufactured tumbled stone.
Field identification & locations
Look for a uniformly dark, fine texture, dense weight, and absence of obvious crystals; a streak test, magnetism test, and inspection for vesicles can help distinguish it. Common worldwide, especially around volcanic regions and ocean beaches.
