igneous
Tumbled dark stone, likely basalt
Basalt; predominantly plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectFine-grained, dark gray to black, with a dull to mildly vitreous luster; typically massive and non-cleaved. Hardness is about 5–6 Mohs and specific gravity about 2.8–3.0; the smooth surface indicates tumbling or polishing.
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Physical properties
Fine-grained, dark gray to black, with a dull to mildly vitreous luster; typically massive and non-cleaved. Hardness is about 5–6 Mohs and specific gravity about 2.8–3.0; the smooth surface indicates tumbling or polishing.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic fields and oceanic crust. Most examples are geologically young, though basalt occurs from Archean rocks to present-day eruptions.
Uses & applications
Used as aggregate, roadstone, building stone, and occasionally as a decorative or meditation stone when polished. Ordinary tumbled pieces have little commercial value.
Geological facts
The specimen’s compact, uniformly dark appearance is consistent with basalt, but the image cannot exclude black chert, slate, or another dark stone without tests.
Field identification & locations
Check for tiny crystalline grains, a streak that is gray rather than metallic, and lack of strong cleavage; basalt is not attracted to a magnet unless it contains abundant magnetite. Common sources include Hawaii, Iceland, India, and oceanic volcanic regions.
