igneous
Vesicular basalt
Basalt; fine-grained mafic volcanic rock composed chiefly of plagioclase, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to brown, dull to faintly subvitreous, with abundant rounded vesicles (gas bubbles); typically hardness 5–6, massive, with no obvious cleavage. The rounded edges indicate natural weathering or water-worn abrasion.
Identified More igneous →
Explore Vesicular basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray to brown, dull to faintly subvitreous, with abundant rounded vesicles (gas bubbles); typically hardness 5–6, massive, with no obvious cleavage. The rounded edges indicate natural weathering or water-worn abrasion.
Formation & geological history
Forms when low-silica basaltic lava cools rapidly at or near Earth’s surface, trapping volcanic gases as vesicles; commonly Cenozoic to modern, though basalt occurs throughout geological time.
Uses & applications
Used as crushed aggregate, road base, riprap, concrete aggregate, and building stone; vesicular varieties are sometimes collected or used decoratively. This ordinary specimen has minimal gem value.
Geological facts
Vesicles may later fill with minerals such as calcite, zeolites, or quartz, producing amygdaloidal basalt. Its high density and dark color distinguish it from pumice, which is much lighter and often floats.
Field identification & locations
Identify by its dark fine-grained matrix, numerous holes, and lack of visible layered grains; test that it is heavy and does not usually scratch glass easily. Common near volcanic fields, lava flows, oceanic crust, and river gravels derived from basalt.
