igneous
Possible basalt or weathered mafic rock
Basalt; chiefly plagioclase feldspar and pyroxene, with possible olivine and iron oxides
AI-generated identification · may be incorrectDark gray to black, fine-grained, dull to weakly subvitreous, with irregular fracture and no obvious cleavage; estimated Mohs hardness 5–6 and specific gravity about 2.8–3.1. The photograph is insufficient to confirm texture or mineral grains.
Identified More igneous →
Explore Possible basalt or weathered 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, dull to weakly subvitreous, with irregular fracture and no obvious cleavage; estimated Mohs hardness 5–6 and specific gravity about 2.8–3.1. The photograph is insufficient to confirm texture or mineral grains.
Formation & geological history
Basalt forms when low-viscosity mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic flows and oceanic crust. Its age could range from recent eruptions to ancient geologic periods.
Uses & applications
Used as crushed aggregate, road base, riprap, railway ballast, building stone, and occasionally polished decorative stone; ordinary pieces have little jewelry value.
Geological facts
Basalt is the most common volcanic rock and makes up much of the ocean floor. Vesicles, magnetic response, and tiny plagioclase crystals are common diagnostic features.
Field identification & locations
Look for a uniformly dark, fine-grained surface, relatively high density, and possible attraction to a magnet from iron-bearing minerals; a fresh edge and hand lens would improve identification. Common worldwide, especially volcanic regions and oceanic terrains.
