Quartzite

Physical Properties

Hardness: 7 (Mohs scale); Color: Gray, tan, white, with some iron staining; Luster: Vitreous to waxy; Crystal Structure: Granular/Trigonal system; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the regional metamorphism of quartzose sandstone. Under intense heat and pressure, the sand grains recrystallize and fuse together. These specimens are typically hundreds of millions to billions of years old.

Uses & Applications

Used primarily in building construction as crushed stone or dimension stone. It is also used as railway ballast and as a source of silica in glass manufacturing. Some aesthetic pieces are used in decorative gravel or lapidary work.

Geological Facts

Quartzite is so tough that it often survives erosion better than other rocks, frequently capping hills and mountain ridges. Unlike sandstone which breaks around its grains, quartzite breaks across the grains due to the complete recrystallization.

Field Identification & Locations

Identify it by its extreme hardness (it will easily scratch glass and steel) and its crystalline, sugary appearance on fresh breaks. It is ubiquitous in mountainous regions and glacial till across North America and Europe.

Identified on: 4/22/2026

Mode: Standard