Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white, gray, or pink (this specimen shows reddish-brown staining from iron oxides); Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None; Specific Gravity: 2.6-2.7.

Formation & Geological History

Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, creating a much harder rock. These can be found in mountain belts worldwide of varying geological ages from Precambrian to Cenozoic.

Uses & Applications

Used in construction as crushed stone for road gravel and railroad ballast, in glass manufacturing if pure enough, and as dimension stone for tiling, countertops, and decorative facades.

Geological Facts

Quartzite is so tough that it often outlasts other surrounding rocks during erosion, frequently forming the tops of ridges and resistant hills called hogbacks. Unlike sandstone, quartzite breaks through its grains rather than around them.

Field Identification & Locations

Identify in the field by its superior hardness (cannot be scratched by a steel nail) and its grainy, sugary appearance on fresh surfaces. It is often found in mountainous regions where tectonic activity was prevalent.

Identified on: 4/25/2026

Mode: Standard