Quartzite Cobble

Physical Properties

Hardness: 7 on Mohs scale; Color: brown to tan due to iron staining; Luster: dull to waxy; Texture: granular, non-foliated; Structure: crystalline; Cleavage: none (conchoidal fracture).

Formation & Geological History

Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. This specimen has been rounded into a 'cobble' through fluvial (river) or glacial abrasion over thousands of years.

Uses & Applications

Used as aggregate in construction, road ballast, and decorative landscaping. High-purity quartzite is used to produce silica sand for glassmaking.

Geological Facts

Quartzite is so tough that it often outlasts the surrounding rock layers during erosion, frequently forming the resistant caps of ridges and mountains.

Field Identification & Locations

Identify in the field by its inability to be scratched by a steel knife and its rounded, smooth surface if found in riverbeds. Common in ancient glacial till and high-energy river systems.

Identified on: 4/15/2026

Mode: Standard