Quartzite

Physical Properties

Hardness: 7 (Mohs scale), Color: Pinkish-red (from iron oxide), Luster: Vitreous to dull, Crystal Structure: Trigonal (granular texture), Cleavage: None (conchoidal fracture)

Formation & Geological History

Formed through the metamorphism of quartz sandstone under high heat and pressure, where quartz grains recrystallize and fuse together. Often Proterozoic or Paleozoic in age.

Uses & Applications

Used in construction as road ballast, railway ballast, and decorative stone. Sometimes used in glass manufacturing if pure.

Geological Facts

Quartzite is so tough that it often survives erosion better than other rocks, forming prominent ridges and hilltops. It is harder than steel and will scratch a glass plate easily.

Field Identification & Locations

Identify by its extreme hardness and the fact that fractures break through the quartz grains rather than around them. Commonly found in riverbeds as rounded 'glacial' cobbles.

Identified on: 5/1/2026

Mode: Standard