igneous
Weathered vesicular basalt (likely amygdaloidal basalt)
Basalt, chiefly plagioclase and pyroxene with possible olivine; cavities may contain secondary zeolites, calcite, or silica
AI-generated identification · may be incorrectDark gray to black, fine-grained, massive igneous rock with abundant weathered cavities and pale mineral infill. Hardness about 5–6 Mohs, dull to faintly vitreous luster, very weak cleavage, and specific gravity around 2.7–3.1.
Identified More igneous →
Explore Weathered vesicular basalt (likely amygdaloidal basalt) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray to black, fine-grained, massive igneous rock with abundant weathered cavities and pale mineral infill. Hardness about 5–6 Mohs, dull to faintly vitreous luster, very weak cleavage, and specific gravity around 2.7–3.1.
Formation & geological history
Forms when low-silica lava cools rapidly at or near Earth’s surface; gas bubbles create vesicles later filled by minerals. The image cannot establish geological age; exposure may represent an ancient lava flow or volcanic fragment deposit.
Uses & applications
Commonly used as crushed aggregate, road base, riprap, railroad ballast, and occasionally building stone. Attractive amygdaloidal pieces are collected or cut for decorative specimens, but these appear ordinary and heavily weathered.
Geological facts
Pale patches may be mineral-filled vesicles rather than true fossils. Basalt is the most abundant volcanic rock on oceanic crust and commonly forms lava flows, dikes, and volcanic plains.
Field identification & locations
Identify by its dark fine-grained matrix, substantial weight, and vesicles; a steel nail generally scratches weathered surfaces but not fresh basalt. Common worldwide in volcanic regions, including oceanic islands and continental lava fields.
