Quartzite

Physical Properties

Hardness: 7 (Mohs scale); Color: Tan, brown, white, or gray; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. These are often found as weathered river stones from ancient mountain belts.

Uses & Applications

Used as crushed stone for road construction, railway ballast, and in the manufacturing of glass and ceramics due to high silica content. Smoother specimens are popular as decorative landscaping pebbles.

Geological Facts

Quartzite is so hard that it will scratch glass. In a true quartzite, the rock will break through the quartz grains rather than around them, distinguishing it from sandstone.

Field Identification & Locations

Identify in the field by its extreme hardness and granular texture. Unlike limestone, it will not fizz with acid. It is commonly found in riverbeds, glacial tills, and mountain ridges where softer rocks have eroded away.

Identified on: 4/17/2026

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