Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, but often yellow, orange, or reddish due to iron oxides; Luster: vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: none (conchoidal fracture).

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. These rocks can date from various geological eras, including the Precambrian.

Uses & Applications

Used primarily in construction as crushed stone for road grit, railroad ballast, and building stone. High-purity quartzite is also used to produce silica sand for glassmaking and industrial silicon metalloids.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rocks during erosion, frequently forming the rugged caps of hills and mountain ranges. It is harder than a steel knife and will easily scratch glass.

Field Identification & Locations

Identify in the field by its extreme hardness and its sugary, granular appearance. Unlike sandstone, it will break across the quartz grains rather than around them. It is ubiquitous in mountainous regions and glacial till.

Identified on: 4/14/2026

Mode: Standard