igneous
Tumbled dark stone, possibly basalt
Basalt; fine-grained mafic rock composed mainly of plagioclase and pyroxene, with possible olivine
AI-generated identification · may be incorrectDark gray-green, rounded and apparently tumbled; typically vitreous to dull luster, hardness about 6 Mohs, massive texture, no visible cleavage, and specific gravity around 2.8–3.0.
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Physical properties
Dark gray-green, rounded and apparently tumbled; typically vitreous to dull luster, hardness about 6 Mohs, massive texture, no visible cleavage, and 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 volcanic fields and oceanic crust; specimens may range from recent to billions of years old.
Uses & applications
Used as aggregate, road stone, riprap, pavers, and occasionally as inexpensive polished decorative stone; this small piece has minimal jewelry value.
Geological facts
The image is insufficient for definitive identification; similar dark tumbled pieces may be andesite, serpentine, slate, or manufactured slag.
Field identification & locations
Test for a uniform fine-grained interior, strong density, and lack of bubbles; a streak, magnetism test, and hardness comparison can help distinguish basalt from slag or softer serpentine. Common worldwide, especially volcanic regions.
