Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: white, gray, with yellowish/brownish iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, original quartz grains recrystallize and fuse together into a dense, hard rock. This specimen appears to be a river-worn or glacial cobble.

Uses & Applications

Used as crushed stone for road construction, railway ballast, and as a decorative stone. High-purity quartzite is used to produce silica sand for glassmaking and industrial abrasives.

Geological Facts

Quartzite is so hard and dense that when it is broken, 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 on a fresh break. Common in mountainous regions and glacial till.

Identified on: 4/27/2026

Mode: Standard