Quartzite Cobble

Physical Properties

Hardness: 7 (Mohs scale); Color: Grayish-yellow, translucent to opaque; Luster: Vitreous/waxy; Structure: Granular/mylonitic; Cleavage: None; SG: 2.6-2.7

Formation & Geological History

Formed from the metamorphism of quartz sandstone under high heat and pressure. This specific specimen is a river-rounded cobble, likely of Paleozoic or Precambrian age, weathered and smoothed by water transport.

Uses & Applications

Used as decorative stone in landscaping, as a railway ballast, in construction as crushed stone, and sometimes as a tool (hammerstone) by prehistoric humans.

Geological Facts

Quartzite is so hard and chemically stable that it often survives in the geological record long after other rocks have eroded away, forming prominent ridges and peaks.

Field Identification & Locations

Identify in the field by its inability to be scratched by steel, its sugary grain texture on a fresh break, and its water-worn, smooth exterior if found in rivers. Found globally in mountainous or glaciated regions.

Identified on: 4/22/2026

Mode: Standard