igneous
Vesicular basalt (likely iron-rich volcanic rock)
Basalt; predominantly plagioclase feldspar, pyroxene, and commonly olivine, with iron oxides
AI-generated identification · may be incorrectDark gray to brown, fine-grained and rough, with abundant gas vesicles; typically dull to slightly glassy. Hardness about 6, no obvious cleavage, and specific gravity roughly 2.7–3.1.
Identified More igneous →
Explore Vesicular basalt (likely iron-rich volcanic rock) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray to brown, fine-grained and rough, with abundant gas vesicles; typically dull to slightly glassy. Hardness about 6, no obvious cleavage, and specific gravity roughly 2.7–3.1.
Formation & geological history
Forms when basaltic lava rapidly cools at or near Earth’s surface, trapping volcanic gases; commonly Cenozoic to Recent, though basalt occurs throughout geological time.
Uses & applications
Used as crushed aggregate, road material, railroad ballast, riprap, and building stone; attractive polished pieces may be sold as decorative specimens. Ordinary fragments have little commercial value.
Geological facts
The rusty brown patches likely represent oxidation of iron-bearing minerals. Vesicles may later fill with secondary minerals such as zeolites, calcite, or quartz, producing amygdaloidal basalt.
Field identification & locations
Identify it by its dark color, fine texture, high density, and rounded holes; it is generally nonreactive with dilute acid and is not strongly magnetic, though iron-rich varieties may attract a magnet. Common in volcanic regions, oceanic crust, Hawaii, Iceland, and the Pacific Northwest.
