Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white, gray, or tan but can be reddish due to iron oxides; Luster: vitreous to grainy; Crystal structure: interlocking quartz grains; Cleavage: none (fractures through grains).

Formation & Geological History

Quartzite forms from the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during tectonic mountain-building events. Most deposits are Proterozoic to Paleozoic in age.

Uses & Applications

Used as a decorative stone in architecture, a source of silica for glassmaking, in construction aggregates, and for railway ballast due to its hardness and durability.

Geological Facts

Quartzite is so tough that it often forms the caps of mountains because it resists erosion much better than the surrounding rock. It is often confused with marble, but quartzite will scratch glass and does not fizz with acid.

Field Identification & Locations

Identify in the field by its extreme hardness and tendency to break through the quartz grains rather than around them (unlike sandstone). Commonly found in folded mountain belts globally.

Identified on: 5/4/2026

Mode: Standard