Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: whitish to yellowish/tan due to iron staining; Luster: vitreous to waxy; Crystal structure: Trigonal (microcrystalline masses); Cleavage: Indistinct; Specific Gravity: 2.6 - 2.65.

Formation & Geological History

Formed when quartz-rich sandstone is subjected to high heat and pressure (metamorphism), causing the sand grains to recrystallize and fuse together into a dense, hard rock. Typically found in mountain belts and shield areas.

Uses & Applications

Used as a decorative stone in landscaping, as a construction aggregate for road ballast, in the production of glass and silicon, and sometimes for decorative items and historical stone tools.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rocks; when broken, quartzite fractures through the quartz grains rather than along their boundaries, unlike its parent rock sandstone.

Field Identification & Locations

Identify in the field by its hardness (it should easily scratch glass) and its granular, sugary texture. It is extremely common in riverbeds and glacial deposits. Look for a lack of layering compared to sedimentary rocks.

Identified on: 4/13/2026

Mode: Standard