igneous
Vesicular basalt (weathered lava rock)
Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine (mafic volcanic rock)
AI-generated identification · may be incorrectDark gray to black, fine-grained, locally vesicular and weathered brown; generally dull to slightly glassy surfaces. Hardness about 5–6 Mohs, no obvious cleavage, dense, with small gas cavities and possible pale feldspar/zeolite fillings.
Identified More igneous →
Explore Vesicular basalt (weathered lava 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, locally vesicular and weathered brown; generally dull to slightly glassy surfaces. Hardness about 5–6 Mohs, no obvious cleavage, dense, with small gas cavities and possible pale feldspar/zeolite fillings.
Formation & geological history
Forms when basaltic lava rapidly cools at or near Earth’s surface, often during volcanic eruptions; individual flows may range from recent to billions of years old. The specimen appears weathered and may contain secondary minerals in vesicles.
Uses & applications
Widely used as crushed aggregate, road metal, riprap, paving stone, and landscaping material; attractive pieces may be collected or used decoratively, though this specimen has modest gem value.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly forms pillow lavas, lava flows, and volcanic plateaus. Its dark color reflects abundant iron- and magnesium-rich minerals.
Field identification & locations
Identify by its black, fine-grained matrix, heavy weight, and occasional vesicles; a hand lens may reveal tiny feldspar laths. Common in volcanic regions, including Hawaii, Iceland, the Pacific Northwest, and oceanic islands.
