Quartzite

Physical Properties

Hardness: 7 (Mohs scale), Color: White, gray, tan, or yellowish due to iron oxides, Luster: Vitreous to waxy, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together into a dense, hard rock. Ages vary widely across geological eras.

Uses & Applications

Used in construction as crushed stone or road ballast, as a raw material for glass making and silica production, and occasionally as decorative landscaping stone or kitchen countertops.

Geological Facts

Quartzite is so hard and durable that it often remains as ridges or peaks after softer surrounding rocks have eroded away. It is often confused with marble but is much harder and will not react with acid.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by steel) and its granular, sugary texture. It is commonly found in mountainous regions or as rounded river cobbles like the one pictured.

Identified on: 4/13/2026

Mode: Standard