metamorphic

River Pebble (Likely Quartzite or Gneiss)

Metamorphosed Silicate Rock (primarily SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5–7 on Mohs scale; Color: Mottled grey, tan, and cream; Luster: Dull to waxy when dry; Structure: Crystalline/Massive (rounded by abrasion); Specific gravity: ~2.65.

Hardness: 6
Color: Mottled grey, tan, and cream
Luster: Dull to waxy when dry

Identified March 24, 2026More metamorphic →

Explore River Pebble (Likely Quartzite or Gneiss) in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 6.5–7 on Mohs scale; Color: Mottled grey, tan, and cream; Luster: Dull to waxy when dry; Structure: Crystalline/Massive (rounded by abrasion); Specific gravity: ~2.65.

Formation & geological history

Formed through the intense heat and pressure of burial (regional metamorphism) of sandstone or granite; later weathered out of parent rock and rounded by transport in a river or glacial environment over thousands of years.

Uses & applications

Common river stones are used broadly in landscaping, as decorative aggregate in construction, and occasionally for lapidary tumbling for beginners.

Geological facts

This specimen is a well-rounded 'clast.' Its smooth, egg-like shape is a result of millions of collisions with other rocks in a high-energy water environment, a process known as saltation.

Field identification & locations

Identify in the field by its smooth, water-worn exterior and lack of sharp edges. These are found in active or ancient riverbeds, beaches, and glacial till. Scratch with a steel file to check hardness; it should resist most steel.