Quartzite

Physical Properties

Hardness: 7 on Mohs scale (scratches glass); Color: White, gray, or tan with yellowish staining; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together into a dense, hard rock. Can range from Precambrian to much younger geological ages.

Uses & Applications

Used in construction as crushed stone for road beds and railway ballast, as a dimension stone for flooring or wall coverings, and in the manufacturing of glass and ceramics due to high silica content.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, forming prominent ridges and hilltops. Unlike its parent rock sandstone, quartzite will break through the quartz grains rather than around them.

Field Identification & Locations

Identify in the field by its extreme hardness and sugary, crystalline texture that does not rub off like sand. Frequently found in mountain ranges or as water-worn cobbles in riverbeds and glacial deposits.

Identified on: 4/25/2026

Mode: Standard