Quartzite

Physical Properties

Hardness: 7 (Mohs scale); Color: Variable, typically white, gray, reddish-pink, or brownish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline masses); Cleavage: None, exhibits conchoidal or irregular fracture; Specific gravity: 2.6–2.7.

Formation & Geological History

Formed through the regional or contact metamorphism of quartzose sandstone. Under high heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, crystalline rock.

Uses & Applications

Used in construction as crushed stone for road ballast, floor tiles, and roofing flakes. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and glass. Also used for decorative stone and countertops.

Geological Facts

Quartzite is so hard that it can scratch steel. Unlike sandstone, which breaks around the individual sand grains, quartzite is so strongly fused that it breaks right through the grains when struck.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and its granular, sugary appearance on fresh surfaces. Often found in mountain ranges or Shield areas where ancient sediments were compressed.

Identified on: 4/15/2026

Mode: Standard