Quartzite

Physical Properties

Hardness: 7 (Mohs scale), Color: pinkish-orange or tan due to iron oxides, Luster: vitreous to dull, Crystal structure: trigonal (microcrystalline), Cleavage: none (fractures across grains), Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz sandstone under high heat and pressure, causing the original quartz grains to recrystallize into a dense, interlocking mosaic.

Uses & Applications

Used in construction as road ballast, gravel, and dimension stone; high-purity varieties are used to produce ferrosilicon and industrial silica sand.

Geological Facts

Quartzite is so tough that it often survives intense erosion cycles, forming the caps of many prominent ridges and hills. It is harder than a steel knife and will easily scratch glass.

Field Identification & Locations

Identify in the field by its extreme hardness and the way it fractures across the component sand grains rather than around them. Commonly found in folded mountain belts.

Identified on: 4/19/2026

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