Quartzite

Physical Properties

Hardness: 7 on Mohs scale; Color: Brownish-tan to reddish-brown (likely due to iron oxide staining); Luster: Vitreous/Glassy when wet or polished; Crystal structure: Hexagonal (as quartz grains); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & Geological History

Formed from the metamorphism of quartz-rich sandstone subjected to high heat and pressure, causing quartz grains to recrystallize and fuse together. It can be found in mountain ranges and areas with ancient tectonic activity.

Uses & Applications

Used as crushed stone for road construction, railroad ballast, and building materials. High-quality pieces are used for countertops, floor tiles, and as decorative landscaping stones.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock during erosion, forming ridges and hilltops. It is one of the hardest commonly available rocks and will easily scratch glass and steel.

Field Identification & Locations

Identify it by its hardness (it should scratch a steel knife blade) and its sugary, crystalline texture where broken. This specimen appears as a river-worn or water-smoothed cobble, likely found in a creek bed or glacial deposit.

Identified on: 4/21/2026

Mode: Standard