igneous
Tumbled dark stone, likely basalt
Basalt (fine-grained mafic volcanic rock; commonly plagioclase, pyroxene, and minor olivine)
AI-generated identification · may be incorrectDark gray to black, rounded and matte-to-subvitreous; typically Mohs 5–6, dense, fine-grained, with no visible cleavage or crystals in this small tumbled specimen.
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Physical properties
Dark gray to black, rounded and matte-to-subvitreous; typically Mohs 5–6, dense, fine-grained, with no visible cleavage or crystals in this small tumbled specimen.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava rapidly cools at or near Earth’s surface, commonly at mid-ocean ridges, hotspots, and volcanic islands. Its age cannot be determined from the image.
Uses & applications
Used as crushed aggregate, road stone, building stone, and landscaping material; polished or tumbled pieces are inexpensive décor and collectible specimens.
Geological facts
Basalt is the most widespread volcanic rock on Earth and forms much of the oceanic crust. Some specimens contain vesicles or small olivine crystals, though none are clearly visible here.
Field identification & locations
Identify it by its uniformly dark color, high density, fine texture, and lack of layering; a streak, magnetism test, and close inspection for tiny crystals would improve identification. Common sources include volcanic regions worldwide.
