igneous
Vesicular basalt (likely scoriaceous basalt)
Basalt; chiefly plagioclase feldspar, clinopyroxene, olivine, and volcanic glass
AI-generated identification · may be incorrectDark gray to black, fine-grained and granular with abundant gas vesicles; typically dull to subtly vitreous, hardness about 5–6 Mohs, no prominent cleavage, and specific gravity roughly 2.7–3.0. The layered, irregular texture may reflect lava flow cooling or weathering.
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Physical properties
Dark gray to black, fine-grained and granular with abundant gas vesicles; typically dull to subtly vitreous, hardness about 5–6 Mohs, no prominent cleavage, and specific gravity roughly 2.7–3.0. The layered, irregular texture may reflect lava flow cooling or weathering.
Formation & geological history
An extrusive mafic igneous rock formed when low-silica lava cooled rapidly at or near Earth’s surface, commonly in volcanic flows; individual specimens may range from recent to Precambrian in age.
Uses & applications
Used as crushed aggregate, road base, riprap, lightweight construction material, and occasionally landscaping stone; attractive pieces are collected but rarely used as gemstones.
Geological facts
Vesicles formed from expanding volcanic gases trapped during cooling; dark metallic-looking grains may be magnetite or weathered ferromagnesian minerals.
Field identification & locations
Identify it by its black color, fine matrix, vesicles, heavy weight, and possible weak magnetism; common in volcanic regions, especially Hawaii, Iceland, the Cascades, and continental rift zones. A precise identification would benefit from a fresh surface and hardness/magnetism tests.
