Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: reddish-brown to white/tan; Luster: vitreous to waxy; Crystal structure: Trigonal (granular); Cleavage: None/Conchoidal fracture; Specific gravity: 2.63-2.65

Formation & Geological History

Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing recrystallization of quartz grains into a dense, interlocking structure.

Uses & Applications

Used as crushed stone for road construction, railroad ballast, and high-purity silica for glassmaking. Smooth samples are popular with rock tumblers and casual collectors.

Geological Facts

Quartzite is so tough that it often survives erosion better than the surrounding rocks, forming prominent ridges and hills. It is often harder than the steel blade of a knife.

Field Identification & Locations

Identify by its extreme hardness (cannot be scratched by steel) and lack of visible grains typical of sandstone. Often found as rounded cobbles in riverbeds or on beaches.

Identified on: 5/3/2026

Mode: Standard