Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, often stained orange/yellow by iron oxides; Luster: vitreous to dull; Crystal structure: 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. High heat and pressure cause the quartz grains to recrystallize and fuse together, creating an extremely durable rock. This process can happen across many geological eras.

Uses & Applications

Used widely in construction as crushed stone for road ballast, floor tiles, and countertop surfaces. Historically used for stone tools due to its hardness and conchoidal fracturing.

Geological Facts

Quartzite is so hard that it will scratch glass and even high-quality steel. It is more resistant to weathering than the surrounding rock, often forming the caps of hills and ridges.

Field Identification & Locations

Identify in the field by its sugary texture on broken surfaces and its ability to scratch glass. It will not fizz with acid (unlike marble). Commonly found in folded mountain belts and ancient cratons.

Identified on: 4/15/2026

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