Quartzite

Physical Properties

Hardness: 7 on Mohs scale. Color: White, grey, or tan (sometimes pink or red due to iron). Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, breaks with a 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 into a dense, crystalline rock. They are found in orogenic belts worldwide.

Uses & Applications

Used as crushed stone for road construction, railway ballast, and as a decorative stone in architecture and landscaping. In high purity forms, it is a source of silica for glassmaking.

Geological Facts

Quartzite is so tough that it often survives intense weathering better than other rocks, frequently forming the caps of ridges and mountains. It is harder than steel and will scratch glass easily.

Field Identification & Locations

Identify by its extreme hardness and the fact that it breaks across the original sand grains rather than around them (unlike sandstone). Commonly found in mountain ranges and glacial deposits. Collectors value highly crystalline or unusually colored pieces.

Identified on: 5/13/2026

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