Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, but often pink or reddish due to iron oxides; Luster: vitreous to dull; Crystal structure: interlocking grains of quartz; Cleavage: none (fractures across grains)

Formation & Geological History

Formed when quartz-rich sandstone is subjected to high heat and pressure (metamorphism). This process causes the original quartz grains to recrystallize and fuse into a solid, hard rock.

Uses & Applications

Used as a decorative stone in construction (countertops, wall cladding), for railway ballast, as a raw material for glass manufacturing, and as a durable outdoor flagstone.

Geological Facts

Quartzite is so hard that it can scratch steel and glass. It is often confused with marble, but marble will react with acid and is much softer. Due to its resistance to erosion, it often forms the caps of ridges and mountains.

Field Identification & Locations

Identify in the field by its sugary texture and extreme hardness (it will scratch a steel knife blade). Look for fractures that cut through the grains rather than around them, which distinguishes it from sandstone.

Identified on: 5/3/2026

Mode: Standard