igneous
Tumbled vesicular basalt
Vesicular basalt, primarily plagioclase, clinopyroxene, olivine, and volcanic glass
AI-generated identification · may be incorrectTypically dark gray to brown, fine-grained, dull to slightly vitreous, with abundant rounded gas vesicles; hardness about 5–6 Mohs, no visible cleavage, and specific gravity roughly 2.4–2.9. The polished/tumbled surface emphasizes the porous texture and weathered brown rind.
Identified More igneous →
Explore Tumbled vesicular basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically dark gray to brown, fine-grained, dull to slightly vitreous, with abundant rounded gas vesicles; hardness about 5–6 Mohs, no visible cleavage, and specific gravity roughly 2.4–2.9. The polished/tumbled surface emphasizes the porous texture and weathered brown rind.
Formation & geological history
An extrusive mafic igneous rock formed when basaltic lava cooled rapidly at or near Earth’s surface, trapping gas bubbles. Its exact age cannot be determined from the image; basalt occurs from Archean rocks to modern volcanic flows.
Uses & applications
Used as aggregate, road stone, landscaping rock, lightweight construction material, and occasionally as a lapidary or aquarium specimen. Common pieces generally have modest collector value.
Geological facts
The holes are vesicles, not fossils; later mineral deposition can fill them to form amygdaloidal basalt. The specimen may also be scoriaceous basalt if it is unusually lightweight and highly porous.
Field identification & locations
Common in volcanic regions, oceanic crust, Hawaii, Iceland, the Pacific Northwest, India’s Deccan Traps, and many basalt quarries. Field identification relies on dark fine grain, vesicles, heavy density, and lack of layering; a magnet may show weak attraction.
