igneous
Dark mafic rock, likely basalt
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine or iron-titanium oxides
AI-generated identification · may be incorrectTypically fine-grained, dark gray to black, with a dull to faintly vitreous luster; hardness about 5–6 Mohs, dense, and lacking visible cleavage. The specimen appears weathered and possibly slightly vesicular, though the image is insufficient for precise identification.
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Physical properties
Typically fine-grained, dark gray to black, with a dull to faintly vitreous luster; hardness about 5–6 Mohs, dense, and lacking visible cleavage. The specimen appears weathered and possibly slightly vesicular, though the image is insufficient for precise identification.
Formation & geological history
Forms when basaltic lava rapidly cools at or near Earth’s surface, commonly in volcanic flows and oceanic crust. It can range from recent eruptions to rocks billions of years old.
Uses & applications
Used as crushed aggregate, road stone, railroad ballast, riprap, and occasionally dimension stone; generally not a jewelry material.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Weathering commonly produces brown, yellow, or reddish iron-oxide staining.
Field identification & locations
Identify by its dark color, high density, fine texture, and inability to scratch easily with a steel knife; a fresh streak is usually gray to black. Common worldwide, especially in Hawaii, Iceland, India’s Deccan Traps, and oceanic regions.
