igneous
Likely weathered basalt
Basalt, a fine-grained mafic volcanic rock composed mainly of plagioclase feldspar and pyroxene, often with minor olivine
AI-generated identification · may be incorrectDark gray-brown, dull to slightly vitreous, dense, and apparently fine-grained; hardness about 5–6 Mohs, with no obvious cleavage or visible crystals. The rough surface and triangular fragment shape appear natural, though a photograph alone cannot confirm the identification.
Identified More igneous →
Explore Likely weathered basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-brown, dull to slightly vitreous, dense, and apparently fine-grained; hardness about 5–6 Mohs, with no obvious cleavage or visible crystals. The rough surface and triangular fragment shape appear natural, though a photograph alone cannot confirm the identification.
Formation & geological history
Basalt forms when low-silica lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, volcanic flows, and flood-basalt provinces. Specimen age depends on locality and may range from recent volcanic material to billions of years old.
Uses & applications
Commonly used as crushed aggregate, road stone, railway ballast, building stone, and occasionally decorative material; unremarkable hand specimens have little jewelry use.
Geological facts
Basalt is the most abundant volcanic rock on Earth and makes up much of the ocean floor. Vesicles, magnetic response, or tiny plagioclase crystals can help distinguish it from other dark rocks.
Field identification & locations
Look for a uniformly dark, heavy, fine-grained texture and possible weak magnetism; test hardness against glass and inspect a fresh fracture. Common worldwide in volcanic regions, especially Hawaii, Iceland, India’s Deccan Traps, and oceanic islands.
