igneous
Tumbled black stone, likely black basalt
Basalt (fine-grained mafic volcanic rock; exact identification requires testing)
AI-generated identification · may be incorrectSmooth, rounded and polished; charcoal-black with a subdued sheen. Basalt is typically Mohs 5–6, fine-grained, and composed mainly of plagioclase feldspar and pyroxene, sometimes with olivine.
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Physical properties
Smooth, rounded and polished; charcoal-black with a subdued sheen. Basalt is typically Mohs 5–6, fine-grained, and composed mainly of plagioclase feldspar and pyroxene, sometimes with olivine.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface; basaltic rocks occur from many geological periods. Tumbling has rounded and polished the specimen.
Uses & applications
Used as a decorative or pocket stone and in landscaping; basalt is also widely used as aggregate and building stone.
Geological facts
A uniformly dark, fine-grained appearance is common in basalt, but other rocks such as slate, chert, or manufactured materials can look similar when polished.
Field identification & locations
Its rounded shape and polish suggest a tumbled specimen, so field texture and hardness are difficult to assess from the image alone. Basalt is common in volcanic regions worldwide.
