Quartzite

Physical Properties

Hardness: 7 on Mohs scale (harder than glass); Color: White, gray, or clouded; Luster: Vitreous to dull; Crystal structure: Trigonal (as quartz grains); Cleavage: None; Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the metamorphism of quartz sandstone under high heat and pressure. This process recrystallizes the quartz grains into a locked, interlocking structure. It is found in mountain-building belts worldwide.

Uses & Applications

Used in construction as road ballast, railway track ballast, and decorative stone. Sometimes used in glass making if the silica content is extremely high.

Geological Facts

Quartzite is one of the most durable and resistant rocks on the Earth's surface. Unlike sandstone, quartzite breaks through the quartz grains rather than around them because the grains are so tightly fused.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sandpaper-like texture that has been fused into a crystalline mass. Common in mountainous regions with historical tectonic activity.

Identified on: 4/20/2026

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