igneous
Rounded gray river pebble, likely basalt or andesite
Fine-grained mafic to intermediate volcanic rock; exact identification requires testing
AI-generated identification · may be incorrectDark gray-brown, smooth and water-worn, dull to weakly vitreous luster, with no visible crystals or cleavage; likely Mohs hardness about 5–6 and specific gravity roughly 2.7–3.0.
Identified More igneous →
Explore Rounded gray river pebble, likely basalt or andesite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-brown, smooth and water-worn, dull to weakly vitreous luster, with no visible crystals or cleavage; likely Mohs hardness about 5–6 and specific gravity roughly 2.7–3.0.
Formation & geological history
Probably formed from rapidly cooled volcanic lava, then eroded and rounded in a stream, beach, or glacial environment. Its precise geological age cannot be determined from the photograph.
Uses & applications
Common material for landscaping, decorative pebble collections, aquarium substrates, and aggregate; generally little commercial or jewelry value.
Geological facts
The pale spot may be a weathered mineral grain, abrasion mark, or surface coating rather than a distinctive mineral. Basalt is typically magnetic to some degree because it commonly contains magnetite.
Field identification & locations
Look for a uniformly fine-grained dark interior, lack of layering, and possible attraction to a magnet; a streak, hardness, density, and fresh fracture would distinguish basalt from andesite, chert, or slag. Common worldwide in volcanic regions and river deposits.
