igneous
Likely tumbled dark igneous stone
Probably basalt or fine-grained gabbro; exact identification is uncertain from the blue-tinted photograph
AI-generated identification · may be incorrectSmall rounded specimen with black to dark gray color, subdued vitreous-to-dull luster, and irregular lighter gray internal patches or faces. Likely hardness about 5–6.5 Mohs, massive texture, no obvious cleavage, and specific gravity roughly 2.8–3.1.
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Physical properties
Small rounded specimen with black to dark gray color, subdued vitreous-to-dull luster, and irregular lighter gray internal patches or faces. Likely hardness about 5–6.5 Mohs, massive texture, no obvious cleavage, and specific gravity roughly 2.8–3.1.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface; gabbro is its slower-cooled intrusive equivalent. These rocks are mostly geologically young in volcanic settings but can occur at any age.
Uses & applications
Commonly used as aggregate, road stone, ballast, and decorative gravel; polished pieces are inexpensive ornamental or teaching specimens.
Geological facts
The apparent blue cast is probably caused by the intense blue lighting or fabric reflection rather than the stone’s true color. Basalt commonly contains plagioclase, pyroxene, and sometimes olivine.
Field identification & locations
In neutral daylight, look for a dense black-gray body, very fine grains, and absence of visible quartz or strong layering; a streak test, magnet test, and specific-gravity measurement would help. Common worldwide in volcanic regions and oceanic crust.
