Quartzite

Physical Properties

Hardness: 7 (Mohs scale), Color: White, gray, or tan (often with yellowish or reddish staining from iron oxidation), Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.65

Formation & Geological History

Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together. It can be found in mountain ranges and ancient shield areas dating from the Proterozoic to more recent eras.

Uses & Applications

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

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock, forming resistant ridges and hilltops. It is one of the hardest and most chemically resistant rocks found at the Earth's surface.

Field Identification & Locations

Identify in the field by its hardness (it will easily scratch glass) and its tendency to break across the original sand grains rather than around them. This distinction separates it from sandstone. Look for it in metamorphic terrains.

Identified on: 4/14/2026

Mode: Standard