Quartzite

Physical Properties

Hardness: 7 (Mohs scale), Color: White, gray, or tan, Luster: Vitreous to dull, Crystal structure: Trigonal/Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high heat and pressure, the individual quartz grains recrystallize and fuse into a dense, interlocking matrix. This material often dates back to various geological eras depending on the source sandstone, ranging from Proterozoic to more recent periods.

Uses & Applications

Used widely in construction as crushed stone for roadbeds or railroad ballast, in landscaping, as dimension stone for counter-tops or flooring, and sometimes as a source of high-purity silica for glassmaking.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rocks in mountainous areas, forming the caps of ridges and peaks. It is significantly harder and more durable than the sandstone from which it originated.

Field Identification & Locations

Identify in the field by its extreme hardness (will scratch glass and steel) and its granular, sugary texture on freshly broken surfaces. Unlike marble, it will not fizz when exposed to acid. It is commonly found in fold mountain belts globally.

Identified on: 4/15/2026

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