Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Pinkish-orange (due to iron oxide inclusions); Luster: Vitreous to dull; Crystal structure: Hexagonal/Trigonal (individual grains); Cleavage: None (conchoidal fracture); SG: 2.6 - 2.65

Formation & Geological History

Formed through the regional metamorphism of quartz sandstone. Intense heat and pressure cause the sand grains to recrystallize and fuse together, forming an interlocking mosaic of quartz crystals. Most often found in mountain belts and Precambrian shields.

Uses & Applications

Used in various construction applications including road ballast, railway tracks, and decorative building stone. It is also used as a source of silica in glass manufacturing and as an abrasive in industrial processes.

Geological Facts

Quartzite is so tough that it often survives erosion better than other rocks, forming prominent ridges or mountain peaks. Unlike sandstone, when quartzite is broken, it fractures through the individual sand grains rather than around them.

Field Identification & Locations

Identify in the field by its extreme hardness (it will easily scratch glass) and granular, sugary appearance on fresh surfaces. Often found in proximity to other metamorphic rocks like schist or gneiss. Look for a dense, non-foliated texture.

Identified on: 4/13/2026

Mode: Standard