Quartzite

Physical Properties

Hardness: 7 (Mohs scale); Color: Reddish-brown, gray, or white; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz sandstone under high heat and pressure, typically in convergent plate boundaries. This specific specimen appears to be a water-worn river cobble.

Uses & Applications

Used in construction as road ballast, railway ballast, and decorative stone. Sometimes used in glassmaking if pure enough.

Geological Facts

Quartzite is so tough that it often survives intense mechanical weathering, resulting in smooth, rounded cobbles like the one shown here that can be transported long distances by rivers.

Field Identification & Locations

Identify in the field by its hardness (it will scratch glass and steel) and its granular, sugary appearance on a fresh break. Commonly found in mountain belts and glacial till.

Identified on: 5/3/2026

Mode: Standard