Quartzite

Physical Properties

Hardness: 7 (Mohs scale); Color: Gray, tan, or pinkish; Luster: Vitreous to dull; Crystal structure: Hexagonal/trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, eliminating pore space.

Uses & Applications

Used as crushed stone for road construction, railway ballast, and as a decorative stone in architecture (countertops and flooring). It is also used as a source of silica for glass and ceramic manufacturing.

Geological Facts

Quartzite is so tough that it often survives intense weathering better than surrounding rocks, frequently forming the tops of ridges and mountains. It is harder than steel and will easily scratch a knife blade.

Field Identification & Locations

Identify in the field by its sugary texture on broken surfaces and its extreme hardness; it will scratch glass and lacks the visible sand grains of its parent sandstone. Commonly found in folded mountain belts globally.

Identified on: 5/3/2026

Mode: Standard