Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, but can be pink or reddish due to iron oxide; Luster: vitreous to dull; Crystal structure: granular, non-foliated; Cleavage: none (breaks with a conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the original quartz grains recrystallize and fuse together into a dense, hard rock. It is found in tectonic belts and mountain ranges worldwide.

Uses & Applications

Used as crushed stone in road construction and railway ballast; cut and polished for floor tiles, countertops, and wall coverings; also used as a source of silica for glass manufacturing.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock in the landscape, forming prominent ridges and peaks. It is sometimes mistaken for marble, but can be distinguished because it will scratch glass and does not fizz in acid.

Field Identification & Locations

Identify in the field by its extreme hardness, sugary texture, and the way it breaks through the quartz grains rather than around them. Commonly found in eroded mountain ranges like the Appalachians or the Alps.

Identified on: 4/30/2026

Mode: Standard