Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Gray, white, or yellowish; 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 under intense heat and pressure, typically during mountain-building events (orogeny). The individual quartz grains recrystallize into a locked mosaic.

Uses & Applications

Used as crushed stone for road construction, railway ballast, and as a raw material in the glass and silicate industries. Polished slabs are used for countertops and flooring.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, forming prominent ridges and peaks. It is frequently mistaken for marble but can be distinguished by its superior hardness.

Field Identification & Locations

Identify in the field by its inability to be scratched by a steel knife and its sugary, granular texture on fresh surfaces. It is found globally in folded mountain belts and ancient shield areas.

Identified on: 4/24/2026

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