Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Yellowish-tan/buff; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None, conchoidal fracture; Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. Most deposits are Proterozoic to Paleozoic in age.

Uses & Applications

Used as a decorative stone in architecture, as crushed stone for road construction and railway ballast, and in the manufacturing of glass and ceramics due to its high silica content.

Geological Facts

Quartzite is so hard that it can easily scratch glass and steel. It is more resistant to weathering than the sandstone it originated from, often forming the caps of ridges and mountains.

Field Identification & Locations

Identify in the field by its extreme hardness and the fact that fractures go through the industrial quartz grains rather than around them (unlike sandstone). Found globally in folded mountain belts like the Appalachians.

Identified on: 5/5/2026

Mode: Standard