igneous
Rounded gray pebble, likely quartz-rich river cobble
Probable granitic or quartzitic cobble; exact identification requires a fresh surface and tests
AI-generated identification · may be incorrectGray-brown, fine- to medium-grained, dull to weakly silky luster, with a pale vein or weathered fracture. Estimated hardness 6–7 Mohs; massive, with no obvious cleavage, and likely specific gravity around 2.6–2.7.
Identified More igneous →
Explore Rounded gray pebble, likely quartz-rich river cobble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Gray-brown, fine- to medium-grained, dull to weakly silky luster, with a pale vein or weathered fracture. Estimated hardness 6–7 Mohs; massive, with no obvious cleavage, and likely specific gravity around 2.6–2.7.
Formation & geological history
Likely formed as durable quartz-bearing rock, then rounded by stream or beach abrasion; its original age cannot be determined from the photograph. The pale band may be quartz or feldspar filling a fracture.
Uses & applications
Mostly a common collecting or decorative pebble; comparable material may be used as aggregate, landscaping stone, or road gravel, but this individual has little commercial value.
Geological facts
The smooth shape indicates prolonged transport or wave action. A glassy, translucent vein that scratches glass would strongly support quartz.
Field identification & locations
Common in riverbeds, beaches, and glacial deposits. Test hardness against glass, inspect a broken or freshly scratched area for visible quartz grains, and use dilute hydrochloric acid only if carbonate rock is suspected.
