igneous
Likely basalt or other dark igneous rock
Basalt; predominantly plagioclase feldspar and pyroxene, possibly olivine
AI-generated identification · may be incorrectDark gray to brown, fine-grained and dull, with no visible crystal faces; typical basalt hardness is about 6 Mohs, dense, and lacking prominent cleavage. The image is blurred, so exact texture and mineral content cannot be confirmed.
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Physical properties
Dark gray to brown, fine-grained and dull, with no visible crystal faces; typical basalt hardness is about 6 Mohs, dense, and lacking prominent cleavage. The image is blurred, so exact texture and mineral content cannot be confirmed.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic flows, oceanic crust, and flood-basalt provinces. Most specimens are geologically young relative to continental rocks, ranging from recent eruptions to billions of years old.
Uses & applications
Used as crushed aggregate, road base, riprap, railroad ballast, concrete aggregate, and building stone; attractive varieties may be polished for décor or collected.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Vesicles, if present, indicate gas-rich lava; magnetic attraction can occur when magnetite is abundant.
Field identification & locations
Commonly found in volcanic regions, river gravels, and coastal exposures; identify it by its dark color, fine texture, high density, and possible tiny vesicles. A fresh surface and a hand lens would improve identification.
