Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, often with reddish or purple tints from iron oxides; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (conchoidal fracture).

Formation & Geological History

Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, causing the original quartz grains to recrystallize and fuse together. Often found in mountain belts (orogenic belts).

Uses & Applications

Used in construction as road ballast, railway ballast, and building stone. Highly durable and resistant to chemical weathering. Crushed quartzite is used in the glass and ceramic industries.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rocks, forming distinctive ridges or mountainous peaks. It is much harder than sandstone and will scratch glass easily.

Field Identification & Locations

Identify in the field by its hardness (7) and 'sugary' texture. Unlike sandstone, when broken, quartzite breaks across the quartz grains rather than around them. Common in Precambrian and Paleozoic geological formations.

Identified on: 4/21/2026

Mode: Standard