igneous
Vesicular basalt (likely olivine basalt)
Basalt; primarily plagioclase, clinopyroxene, olivine, and volcanic glass
AI-generated identification · may be incorrectDark gray-green, fine-grained, porous, and generally dull to weakly vitreous; hardness about 5–6 Mohs, with no obvious cleavage and typical specific gravity around 2.8–3.0. The pale rounded spots are likely vesicles lined or partly filled with secondary minerals such as calcite or zeolites.
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Physical properties
Dark gray-green, fine-grained, porous, and generally dull to weakly vitreous; hardness about 5–6 Mohs, with no obvious cleavage and typical specific gravity around 2.8–3.0. The pale rounded spots are likely vesicles lined or partly filled with secondary minerals such as calcite or zeolites.
Formation & geological history
An extrusive igneous rock formed when mafic lava cooled rapidly at or near Earth’s surface; commonly Cenozoic to older, depending on locality. Vesicles formed from gas bubbles trapped during eruption, later altered by groundwater.
Uses & applications
Used extensively as crushed aggregate, road base, riprap, concrete additive, and lightweight landscaping stone; attractive pieces are collected but are rarely gem-grade.
Geological facts
Its green coloration may reflect olivine, chlorite, or weathering. A magnet may show weak attraction if magnetite is abundant, and a fresh broken surface is typically black-gray and fine-grained.
Field identification & locations
Look for a dense, dark matrix with small cavities, absence of visible large crystals, and a heavy feel; common in volcanic regions, oceanic crust, Hawaii, Iceland, the Pacific Northwest, and continental basalt fields. Exact identification would benefit from a fresh surface, hardness test, and acid test on the cavity fillings.
