igneous
River Pebble (Granite/Gneiss)
Granitic Pebble / Quartz-Feldspar Aggregate
Hardness around 6-7 on Mohs scale. Color ranges from grey to brownish-grey with speckles of quartz, feldspar, and biotite mica. Dull, earthy to slightly sugary texture, rounded and smoothed by water erosion.
Identified More igneous →
Explore River Pebble (Granite/Gneiss) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness around 6-7 on Mohs scale. Color ranges from grey to brownish-grey with speckles of quartz, feldspar, and biotite mica. Dull, earthy to slightly sugary texture, rounded and smoothed by water erosion.
Formation & geological history
Formed through the cooling and crystallization of felsic magma deep underground, or through high-grade regional metamorphism. Subsequently eroded from bedrock and rounded over thousands of years in riverbeds, lakes, or coastal currents.
Uses & applications
Commonly used in landscaping, river rock decor, aggregate for concrete, aquarium decoration, and general rock tumbling projects.
Geological facts
Smooth river rocks acquire their rounded shapes over long periods due to attrition—clashing against other stones in moving water—which wears away sharp edges and corners.
Field identification & locations
Identified by its well-rounded, elongated cobble shape, dull surface, and visible coarse mineral grains (granitic texture) under magnification. Found in riverbeds, glacial tills, and alluvial deposits worldwide.
