Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Tan, beige, or white; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Specific gravity: 2.6–2.7

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, creating a density that eliminates the original pore spaces.

Uses & Applications

Used in construction as road ballast, gravel, and dimension stone. High-purity quartzite is used to produce silica sand for glassmaking and silicon for electronics.

Geological Facts

Quartzite is so tough that it often survives intense erosion to form the crests of mountain ridges. Unlike sandstone, which breaks around grains, quartzite breaks through the grains due to its uniform recrystallization.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by steel) and its grainy, sugary appearance on fresh fractures. It is commonly found in ancient mountain belts and riverbeds as rounded cobbles.

Identified on: 4/27/2026

Mode: Standard