igneous
Likely weathered basalt or dark metamorphic rock
Fine-grained mafic rock, probably basalt (plagioclase + pyroxene ± olivine)
AI-generated identification · may be incorrectDark brown-gray, dull to slightly vitreous, fine-grained, and irregularly fractured; estimated Mohs hardness 5–6, with no obvious cleavage or visible crystals. The image is insufficient for confident mineral identification.
Identified More igneous →
Explore Likely weathered basalt or dark metamorphic rock in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark brown-gray, dull to slightly vitreous, fine-grained, and irregularly fractured; estimated Mohs hardness 5–6, with no obvious cleavage or visible crystals. The image is insufficient for confident mineral identification.
Formation & geological history
If basalt, it formed from rapidly cooled mafic lava, commonly in volcanic flows, generally at any age from Archean to modern. Weathering appears to have altered its surface to brown tones.
Uses & applications
Common basalt is used for aggregate, roadstone, concrete, and occasionally decorative stone; this small specimen has mainly educational or collecting value.
Geological facts
A streak test, fresh broken surface, magnet test, and close examination for vesicles or crystals would help distinguish basalt from slate, hornfels, or other dark rocks.
Field identification & locations
Look for a dense, fine-grained texture and dark fresh interior; basalt may be weakly magnetic and usually does not fizz with dilute hydrochloric acid. Common worldwide, especially near volcanic regions.
