igneous
Dark rounded river pebble (likely basalt)
Basalt, a fine-grained mafic volcanic rock; identification is tentative from the photo.
AI-generated identification · may be incorrectDark gray-brown, rounded and weathered, with a dull surface and no visible crystals. Basalt is typically composed of plagioclase and pyroxene, sometimes olivine; hardness is about 5–6 Mohs and its minerals have no prominent cleavage.
Identified More igneous →
Explore Dark rounded river pebble (likely basalt) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-brown, rounded and weathered, with a dull surface and no visible crystals. Basalt is typically composed of plagioclase and pyroxene, sometimes olivine; hardness is about 5–6 Mohs and its minerals have no prominent cleavage.
Formation & geological history
Likely formed when basaltic lava cooled rapidly at or near the surface, then became rounded by water abrasion. Its age cannot be determined from appearance alone.
Uses & applications
Commonly used as crushed aggregate, road stone, and construction material; a pebble of this size is mainly suitable for collecting or decoration.
Geological facts
Basalt is among Earth’s most abundant volcanic rocks and also forms much of the ocean floor.
Field identification & locations
Its dark color, fine-grained texture, and lack of visible layering fit basalt, but the photo does not show diagnostic mineral details. Rounded pebbles occur in rivers and on beaches worldwide.
