igneous
Weathered volcanic rock, likely basalt or andesite
Fine-grained mafic to intermediate volcanic rock; primarily plagioclase feldspar, pyroxene, and possibly olivine or iron oxides
AI-generated identification · may be incorrectDark brown to gray, rounded and weathered, with a dull to subtly earthy luster and small pits or vesicles; likely hardness about 5–6 Mohs, no obvious cleavage, and fine-grained texture. Exact identification requires a fresh surface, streak, magnetism, and mineral examination.
Identified More igneous →
Explore Weathered volcanic rock, likely basalt or andesite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark brown to gray, rounded and weathered, with a dull to subtly earthy luster and small pits or vesicles; likely hardness about 5–6 Mohs, no obvious cleavage, and fine-grained texture. Exact identification requires a fresh surface, streak, magnetism, and mineral examination.
Formation & geological history
Formed when lava cooled at or near Earth’s surface, probably during a volcanic episode; its specific geological age cannot be determined from the photograph. Rounding and surface alteration indicate transport in a stream, beach, or glacial setting.
Uses & applications
Common basalt and andesite are used as crushed aggregate, road stone, riprap, and building stone; this small specimen has mainly educational or modest collecting value.
Geological facts
The brown coloration likely results from weathering of iron-bearing minerals to oxides. Vesicles, if confirmed, indicate gas bubbles trapped in cooling lava.
Field identification & locations
Common in volcanic regions and river or beach gravels worldwide; test with a steel nail, magnet, and dilute acid, and inspect a chipped surface for its true color and texture. It could also be a weathered metamorphic or sedimentary pebble, so a definitive name is not possible visually.
