igneous
Weathered basalt pebble
Basalt, a fine-grained mafic volcanic rock composed mainly of plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectDark gray to brown, dull to subtly vitreous, fine-grained, and rounded by abrasion; hardness about 5–6 Mohs, with no obvious cleavage. Small pits may represent vesicles or weathered mineral grains; specific gravity is typically about 2.8–3.0.
Identified More igneous →
Explore Weathered basalt pebble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray to brown, dull to subtly vitreous, fine-grained, and rounded by abrasion; hardness about 5–6 Mohs, with no obvious cleavage. Small pits may represent vesicles or weathered mineral grains; specific gravity is typically about 2.8–3.0.
Formation & geological history
Formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, commonly during Cenozoic or older volcanic activity; the pebble was later transported and weathered in a stream, beach, or gravel deposit.
Uses & applications
Used extensively as crushed aggregate, road material, riprap, railroad ballast, and landscaping stone; this small weathered specimen has mainly educational or modest collecting value.
Geological facts
Basalt is Earth’s most abundant volcanic rock and forms much of the oceanic crust, including the seafloor and many volcanic islands.
Field identification & locations
Identify it by its dark color, high density, fine texture, and lack of visible large crystals; common sources include Hawaii, Iceland, oceanic islands, volcanic mountain belts, and basalt-bearing river or beach gravels.
