Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to grey, often with reddish-brown staining from iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, breaks with conchoidal fracture.

Formation & Geological History

Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high temperatures and pressures, individual quartz grains recrystallize into a dense interlocking mosaic.

Uses & Applications

Commonly used as crushed stone for road construction, railroad ballast, and as a decorative building stone or countertop material. High-purity quartzite is also a source of silica for glass manufacturing.

Geological Facts

Quartzite is so tough that it often survives intense weathering better than other rocks, frequently forming the caps of ridges and hills. It is often confused with marble, but quartzite will not fizz in acid and is much harder.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and its tendency to break through the quartz grains rather than around them (unlike sandstone). Commonly found in mountain belts and Precambrian shield areas.

Identified on: 5/3/2026

Mode: Standard