Quartzite

Physical Properties

Hardness: 7 on Mohs scale (scratches glass); Color: White, gray, pinkish or reddish due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular 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. Extreme heat and pressure cause the quartz grains to recrystallize and fuse together. Often found in Precambrian formations over 500 million years old.

Uses & Applications

Used as crushed stone for road construction, railway ballast, and as a raw material in glass manufacturing. High-purity quartzite is used to produce ferrosilicon and industrial silica.

Geological Facts

Quartzite is so tough that it often survives intense weathering and glacial transport, resulting in the rounded 'cobble' shape seen in this specimen. It is one of the most durable rocks found on the Earth's surface.

Field Identification & Locations

Identify in the field by its inability to be scratched by a steel knife and its sugary, granular texture. Unlike marble, it will not fizz with acid. Common in mountainous regions and glacial drift areas.

Identified on: 4/25/2026

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