metamorphic

Quartzite (River Pebble)

Metamorphosed Quartz Sandstone (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Grayish-white with yellow/orange iron staining; Luster: Vitreous to dull; Crystal structure: Granoblastic (crystalline); Cleavage: None (conchoidal fracture)

Hardness: 7 (Mohs scale)
Color: Grayish-white with yellow/orange iron staining
Luster: Vitreous to dull

Identified July 1, 2026More metamorphic →

Explore Quartzite (River Pebble) in the encyclopedia →

Identify your own rocks.

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

App Store Google Play

Physical properties

Hardness: 7 (Mohs scale); Color: Grayish-white with yellow/orange iron staining; Luster: Vitreous to dull; Crystal structure: Granoblastic (crystalline); Cleavage: None (conchoidal fracture)

Formation & geological history

Formed when quartz-rich sandstone is subjected to high heat and pressure, causing the sand grains to recrystallize into a dense, hard metamorphic rock. This specific specimen has been rounded by fluvial (river) erosion.

Uses & applications

Construction aggregate, railroad ballast, decorative landscaping, and occasionally used as a source of high-purity silica for glassmaking.

Geological facts

Quartzite is so hard and chemically resistant that it often forms the caps of mountains and ridges. It is harder than steel; a steel knife will not scratch it, but the rock will scratch the knife.

Field identification & locations

Identified in the field by its sugary texture, extreme hardness, and lack of reaction to acid. Commonly found in riverbeds, glacial deposits, and ancient mountain belts.