Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white to gray, often pink or reddish due to iron oxides; Luster: glassy to dull; Structure: non-foliated, interlocking quartz crystals; Cleavage: none (fractures conchoidally)

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, usually at convergent plate boundaries. This causes the original sand grains to recrystallize into a dense, interlocking mosaic.

Uses & Applications

Used in construction as crushed stone for road grit and railroad ballast, in architecture as decorative stone or countertops, and as a source of silica in glass manufacturing.

Geological Facts

Quartzite is so durable that it often forms the resistant caps of ridges and mountain ranges. It is harder than the steel of a pocketknife, which is a key way to distinguish it from similar-looking marble.

Field Identification & Locations

Identify in the field by its extreme hardness (it will scratch glass) and its sugary, crystalline texture that breaks through the grains rather than around them. Found globally in ancient mountain belts.

Identified on: 4/15/2026

Mode: Standard