igneous
Polished black stone, likely basalt or fine-grained mafic rock
Basalt (probable; identification uncertain from photograph)
AI-generated identification · may be incorrectDark gray to black, fine-grained, compact, and weakly to moderately reflective from polishing; typically Mohs 6, with no visible cleavage and an interlocking microscopic crystal texture. Common minerals are plagioclase, pyroxene, and sometimes olivine or magnetite.
Identified More igneous →
Explore Polished black stone, likely basalt or fine-grained mafic rock in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray to black, fine-grained, compact, and weakly to moderately reflective from polishing; typically Mohs 6, with no visible cleavage and an interlocking microscopic crystal texture. Common minerals are plagioclase, pyroxene, and sometimes olivine or magnetite.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in volcanic fields and oceanic crust. Its exact geological age cannot be determined visually; polished shaping indicates human processing.
Uses & applications
Used as a decorative/tumbled stone, aggregate, paving material, building stone, and occasionally in carvings. Ordinary polished pieces have modest collector value.
Geological facts
The elongated, smoothly rounded form appears shaped and polished rather than naturally weathered. Similar-looking materials include black chert, gabbro, slate, and industrial slag.
Field identification & locations
Basalt is commonly found in volcanic regions, including Hawaii, Iceland, India, the western United States, and ocean basins. A streak test, magnetism test, density, and close examination for crystals or vesicles would help distinguish it from chert or slag.
