Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Brown, tan, or grayish due to iron impurities; 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 quartzose sandstone. Under high heat and pressure, the original quartz grains recrystallize and fuse together into a dense, hard rock. Can range from Proterozoic to more recent geological ages.

Uses & Applications

Used in construction as road ballast, gravel, and dimension stone; high-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock layers, forming prominent ridges and peaks in mountain ranges. It is harder than a steel knife and will easily scratch glass.

Field Identification & Locations

Identify in the field by its hardness (it cannot be scratched by steel) and its grainy, sandpaper-like texture that lacks the individual distinct grains of sandstone because they have fused. Commonly found in folded mountain belts globally.

Identified on: 4/22/2026

Mode: Standard