metamorphic
Quartzite Cobble
Metamorphosed sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white with brownish iron staining; Luster: Dull to vitreous; Crystal structure: Granular crystalline; Cleavage: None (breaks across grains)
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white with brownish iron staining
- Luster
- Dull to vitreous
Identified More metamorphic →
Explore Quartzite Cobble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white with brownish iron staining; Luster: Dull to vitreous; Crystal structure: Granular crystalline; Cleavage: None (breaks across grains)
Formation & geological history
Formed when quartz-rich sandstone is subjected to heat, pressure, and chemical activity of metamorphism, recrystallizing the silica grains. Often found as rounded river stones or glacial till.
Uses & applications
Primarily used in construction (crushed stone), as railway ballast, and in some industrial applications for silica; popular for landscaping or as simple decorative river rocks.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains because it resists erosion better than surrounding rocks.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and a sugary, crystalline appearance on a fresh break. Commonly found in riverbeds, beaches, and glacial deposits.
More like this
