Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: typically white, gray, or tan but can be reddish; Luster: vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: none (conchoidal fracture).

Formation & Geological History

Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure reciprocal to tectonic activity cause the sand grains to recrystallize and fuse together. These are globally ancient rocks often associated with mountain ranges.

Uses & Applications

Used as crushed stone for road construction and railway ballast. Due to its hardness, it is also used for floor tiles, countertops, and decorative carvings.

Geological Facts

Quartzite is so hard that when it breaks, it fractures through the quartz grains rather than along the boundaries between them, unlike its parent rock, sandstone.

Field Identification & Locations

Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its crystalline, sugary appearance. It is commonly found in beach or river cobbles and used as a durable building material.

Identified on: 4/24/2026

Mode: Standard