Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Gray, white, or tan; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (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. Under intense heat and pressure, the original quartz grains recrystallize and fuse together, creating an extremely hard and durable rock.

Uses & Applications

Used as crushed stone for road construction, railway ballast, and as a decorative stone in architecture. High-purity quartzite is used to produce silica sand for glassmaking and silicon for electronics.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock layers during erosion, frequently forming the peaks of mountains and ridges. It is often confused with marble, but can be distinguished because quartzite will not react with acid.

Field Identification & Locations

Identify in the field by its extreme hardness (will scratch glass and steel) and its grainy, sugary texture. Unlike sandstone, quartzite fractures across the original sand grains rather than around them. Common in metamorphic belts worldwide.

Identified on: 4/30/2026

Mode: Standard