igneous
Tumbled basalt (likely vesicular basalt)
Basalt; primarily plagioclase, clinopyroxene, and olivine, with iron oxides
AI-generated identification · may be incorrectDark gray to black, locally brown-weathered, with a smooth rounded surface and subtle vesicles or altered patches; typically fine-grained, compact, dull to weakly vitreous, Mohs hardness about 5–6, and specific gravity 2.8–3.0. The image is insufficient to confirm the exact rock or minerals.
Identified More igneous →
Explore Tumbled basalt (likely vesicular basalt) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray to black, locally brown-weathered, with a smooth rounded surface and subtle vesicles or altered patches; typically fine-grained, compact, dull to weakly vitreous, Mohs hardness about 5–6, and specific gravity 2.8–3.0. The image is insufficient to confirm the exact rock or minerals.
Formation & geological history
Basalt forms when low-silica lava rapidly cools at or near Earth’s surface, commonly in volcanic flows, oceanic crust, and hotspots. Specimen age could range from recent volcanic material to ancient basalt; tumbling is human processing.
Uses & applications
Used extensively as crushed aggregate, road stone, paving, riprap, and construction material; attractive polished pieces are sold as curios or cabochon-like specimens. Common specimens usually have modest commercial value.
Geological facts
Basalt is the most common volcanic rock and makes up much of the ocean floor. Brown or green areas may represent weathering, iron oxidation, or alteration minerals rather than the primary basalt.
Field identification & locations
Common worldwide, especially in volcanic regions, oceanic islands, and flood-basalt provinces. Field identification relies on dark fine grain, high density, lack of obvious quartz, and possible tiny gas cavities; a fresh surface and streak/magnet test can help.
