igneous
Likely vesicular basalt
Basalt, a fine-grained mafic volcanic rock; commonly composed of plagioclase, pyroxene, and minor olivine
AI-generated identification · may be incorrectDark gray, fine-grained, dull to slightly earthy luster, with possible small vesicles and weathered pale surface; hardness about 5–6, generally massive with no obvious cleavage. The image is insufficient for confident mineral-level identification.
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Physical properties
Dark gray, fine-grained, dull to slightly earthy luster, with possible small vesicles and weathered pale surface; hardness about 5–6, generally massive with no obvious cleavage. The image is insufficient for confident mineral-level identification.
Formation & geological history
Forms when basaltic lava rapidly cools at or near Earth’s surface, commonly in volcanic flows; specimens may range from recent eruptions to Archean rocks over 2.5 billion years old.
Uses & applications
Widely used as crushed aggregate, road base, railway ballast, riprap, and building stone; attractive polished basalt is also used decoratively.
Geological facts
Basalt is the most abundant volcanic rock on Earth and makes up much of the oceanic crust. Vesicles form when gas bubbles are trapped during cooling.
Field identification & locations
Look for a dense dark color, fine texture, and abundant plagioclase/pyroxene; a streak test, hand lens, and specific-gravity test help distinguish it from scoria or weathered andesite. Common worldwide, especially volcanic regions and oceanic islands.
