Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, often tan, yellow, or reddish due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. It can be found in mountain belts and areas of intense tectonic activity.

Uses & Applications

Used as crushed stone for road construction, railroad ballast, and as a decorative building stone. High-purity quartzite is used in the manufacturing of glass and silicon metal.

Geological Facts

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

Field Identification & Locations

Can be identified in the field by its extreme hardness and the fact that it breaks through the grain rather than around it like sandstone. Common in riverbeds as rounded cobbles or in craggy outcroppings.

Identified on: 5/5/2026

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