igneous
Likely basalt or mafic metamorphic rock
Fine-grained basalt, possibly altered; chiefly plagioclase feldspar and pyroxene, with minor iron-titanium oxides
AI-generated identification · may be incorrectDark gray to black, fine-grained and weakly granular, with dull to faintly submetallic luster; hardness about 5–6, no obvious cleavage, and typical specific gravity around 2.8–3.1. The specimen appears naturally rough rather than polished.
Identified More igneous →
Explore Likely basalt or mafic metamorphic 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 and weakly granular, with dull to faintly submetallic luster; hardness about 5–6, no obvious cleavage, and typical specific gravity around 2.8–3.1. The specimen appears naturally rough rather than polished.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in volcanic flows and oceanic crust; most examples range from Precambrian to modern age. The image alone cannot establish its precise age or exclude a dark metamorphic rock.
Uses & applications
Common basalt is used as crushed aggregate, road base, concrete material, building stone, and occasionally decorative stone; this small piece has little jewelry value.
Geological facts
Basalt is Earth’s most abundant volcanic rock and commonly contains microscopic crystals that require magnification to distinguish. Vesicles, if present, indicate gas bubbles trapped during cooling.
Field identification & locations
Look for a dense dark matrix, tiny interlocking crystals, and possible magnetism from iron oxides; a streak, fresh fracture, and hand lens would improve identification. Common worldwide, especially Hawaii, Iceland, India, and oceanic volcanic regions.
