Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (red/brown staining from iron oxide); Luster: vitreous (glassy) to dull; Crystal structure: hexagonal (cryptocrystalline in texture); Cleavage: none, fractures conchoidally; Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original sand grains to recrystallize and fuse together into a dense, interlocking mosaic of quartz crystals.

Uses & Applications

Used as a decorative stone in architecture, a source of silica for glass manufacturing, crushed stone for road construction and railway ballast, and occasionally in jewelry as cabochons.

Geological Facts

Quartzite is so tough that it often survives intense erosion to form the crests of mountain ridges. Unlike sandstone, which breaks around its grains, quartzite breaks through the grains due to its extreme hardness and density.

Field Identification & Locations

Identify in the field by its inability to be scratched by a steel knife and its sugary, sparkling appearance on a fresh break. Commonly found in folded mountain belts globally, such as the Appalachian Mountains or the Alps.

Identified on: 4/23/2026

Mode: Standard