Quartzite

Physical Properties

Hardness: 7 on Mohs scale. Color: White, gray, pink, or reddish-brown due to iron impurities. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.6–2.7.

Formation & Geological History

Formed when quartz-rich sandstone is subjected to high heat and pressure (metamorphism). This process causes the original quartz grains to recrystallize and fuse together into a dense, hard rock. It can be found in mountain belts globally.

Uses & Applications

Used in construction as crushed stone for road beds, as railway ballast, and as a dimension stone for flooring, walls, and countertops. It is also used as a source of silica for glass manufacturing.

Geological Facts

Quartzite is so hard and durable that it often remains as ridges or peaks on mountains after softer surrounding rocks have eroded away. It is often confused with marble, but can be distinguished by its ability to scratch glass.

Field Identification & Locations

Identify in the field by its extreme hardness (scratches steel) and its grainy, sandpaper-like texture that has been fused into a crystalline mass. It is commonly found in river beds as rounded cobbles or in massive mountain outcrops.

Identified on: 4/27/2026

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