Quartzite

Physical Properties

Hardness: 7 on Mohs scale. Color: White, gray, or tan with iron staining. Luster: Vitreous to dull. Crystal structure: Hexagonal/trigonal. Specific gravity: 2.6-2.7. Cleavage: Indistinct/Conchoidal fracture.

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, the sand grains recrystallize and fuse together into a dense, crystalline rock. Most often found in orogenic (mountain-building) belts.

Uses & Applications

Used in construction as road ballast, gravel, and dimension stone for flooring or countertops. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rocks; it frequently forms the caps of ridges and mountains because it resists weathering so effectively.

Field Identification & Locations

Identify in the field by its grainy, sugary texture and extreme hardness (it will easily scratch glass). Unlike limestone, it will not fizz in contact with hydrochloric acid. Commonly found in mountainous regions or as rounded river cobbles.

Identified on: 5/11/2026

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