Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Off-white, grey, or yellowish; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & Geological History

Formed through the metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events (orogeny). Often found in Precambrian and Paleozoic strata.

Uses & Applications

Used in construction as crushed stone, road ballast, and decorative stone. Historically used for making stone tools. High-purity quartzite is used to produce silica sand for glassmaking.

Geological Facts

Quartzite is so hard and chemically resistant that it often forms the peaks of ridges and mountain ranges because it weathers much more slowly than surrounding rocks.

Field Identification & Locations

Identify in the field by its ability to scratch glass and its grainy, sandpaper-like texture that does not rub off. It breaks across the quartz grains rather than around them. Common in mountainous regions like the Appalachians or the Alps.

Identified on: 4/15/2026

Mode: Standard