Quartzite

Physical Properties

Hardness: 7 on the Mohs scale. Color: White, gray, or reddish-brown due to iron oxide impurities. Luster: Vitreous to dull. Crystal structure: Trigonal (microcrystalline grains). Cleavage: None; breaks with a conchoidal fracture through the grains.

Formation & Geological History

Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize, interlocking to create a dense, hard rock. Typical geological ages range from Precambrian to Mesozoic.

Uses & Applications

Used heavily in construction as crushed stone for road ballast, floor tiles, and countertop surfaces. Also used as a source of silica for glass manufacturing and occasionally as an ornamental stone in landscaping.

Geological Facts

Quartzite is so hard that it can scratch steel and glass easily. In some mountain ranges, quartzite forms the ridge crests because it is extremely resistant to weathering compared to surrounding softer rocks.

Field Identification & Locations

Identify in the field by its grainy, sandpaper-like appearance but glassy feel. Unlike sandstone, quartzite breaks *through* the quartz grains rather than *around* them. Found worldwide in mountainous regions like the Appalachians (USA) or the Alps (Europe).

Identified on: 4/14/2026

Mode: Standard