Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Tan, beige, or yellowish-white; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone. High heat and pressure reciprocal to tectonic compression cause quartz grains to recrystallize and fuse into a dense rock. It can range from Precambrian to Cenozoic in age.

Uses & Applications

Used as crushed stone for road construction, railroad ballast, and building stone. High-purity quartzite is used to produce silica sand for glass making and metallurgy.

Geological Facts

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

Field Identification & Locations

Identify in the field by its hardness (it scratches glass) and its sugary texture. Unlike sandstone, quartzite breaks through the quartz grains rather than around them. It is commonly found in mountainous regions or as rounded river cobbles.

Identified on: 4/29/2026

Mode: Standard