igneous
Basalt (vesicular/amygdaloidal volcanic rock)
Basalt; chiefly plagioclase feldspar, clinopyroxene, and often olivine, with possible iron-oxide alteration
AI-generated identification · may be incorrectDark gray to black, fine-grained, commonly weakly vesicular, with a dull to slightly glassy luster; hardness about 5–6 Mohs, no prominent cleavage, and typical specific gravity 2.8–3.0. The granular, bubbly texture is consistent with rapidly cooled lava.
Identified More igneous →
Explore Basalt (vesicular/amygdaloidal volcanic rock) 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, commonly weakly vesicular, with a dull to slightly glassy luster; hardness about 5–6 Mohs, no prominent cleavage, and typical specific gravity 2.8–3.0. The granular, bubbly texture is consistent with rapidly cooled lava.
Formation & geological history
Formed when mafic lava erupted and cooled at or near Earth’s surface, commonly during Cenozoic or older volcanic activity; its exact age cannot be determined from the image.
Uses & applications
Widely used as crushed aggregate, road base, railroad ballast, riprap, and building stone; attractive polished pieces are used decoratively, though this specimen appears mainly of collecting or teaching value.
Geological facts
Basalt is the most abundant volcanic rock in oceanic crust and forms much of the seafloor, mid-ocean ridges, and many lava plateaus.
Field identification & locations
Identify it by its black fine-grained matrix, heavy feel, and lack of visible large crystals; a streak, fresh fracture, and hand lens help distinguish it from scoria, slag, or weathered industrial material. Common localities include Hawaii, Iceland, the Columbia River Basalt Province, and oceanic volcanic islands.
