Quartzite

Physical Properties

Hardness: 7 Mohs scale; Color: Reddish-brown, gray, pink; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); 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 quartz grains to recrystallize and fuse together.

Uses & Applications

Used as crushed stone in road construction, railway ballast, and as a decorative stone in landscaping and flooring due to its extreme durability. Some high-purity varieties are used to make glass.

Geological Facts

Quartzite is so hard and durable that it often forms the caprock of mountain ridges. Unlike sandstone, which breaks around individual sand grains, quartzite breaks through the grains.

Field Identification & Locations

Identify by its extreme hardness (cannot be scratched by a steel nail) and the way it breaks along sharp, jagged edges through the crystals. Found globally in fold mountain belts.

Identified on: 5/3/2026

Mode: Standard