Quartzite Cobble

Physical Properties

Hardness: 7 on Mohs scale; Color: reddish-brown surface oxidation with a tan-gray interior; Luster: dull to vitreous; Structure: granular/crystalline texture; Cleavage: none (conchoidal fracture).

Formation & Geological History

Formed from the regional metamorphism of quartz sandstone. The rounded shape indicates secondary weathering as a river-worn cobble or pebble. Formed over millions of years under high pressure and temperature.

Uses & Applications

Used primarily as construction aggregate, railway ballast, and occasionally for primitive stone tools due to its hardness and durability.

Geological Facts

Quartzite is one of the most durable rocks on Earth's surface. This specific specimen shows 'desert varnish' or iron-oxide staining on its exterior from environmental exposure.

Field Identification & Locations

Identify in the field by its inability to be scratched by steel and its granular texture that looks like sandpaper but feels smooth on the weathered surface. Common in riverbeds and mountainous glacial deposits.

Identified on: 4/30/2026

Mode: Standard