Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white, gray, or pinkish/purple due to iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: none, breaks with 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 sand grains to recrystallize and fuse into a dense, hard rock. Various ages from Precambrian to Cenozoic.

Uses & Applications

Used as crushed stone for road construction, railroad ballast, decorative building stone, and floor tiles. High-purity quartzite is used to produce silica sand for glassmaking and silicon for industrial electronics.

Geological Facts

Quartzite is so tough that it often survives intense weathering better than other rocks, frequently forming the tops of ridges and mountains. It is harder than a steel knife and will scratch glass easily.

Field Identification & Locations

Identify in the field by its sugary, granular texture and its inability to be scratched by a steel blade. It differs from sandstone because it breaks across the grains rather than around them. Found globally in mountainous regions.

Identified on: 4/29/2026

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