River Cobble (Quartzite and Iron-stained Quartz)

Physical Properties

Hardness: 7 (Mohs scale), Color: White, tan, and reddish-brown, Luster: Vitreous to dull, Crystal Structure: Hexagonal (microcrystalline), Cleavage: None/Conchoidal fracture, Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the metamorphism of quartz sandstone under high heat and pressure, subsequently eroded and rounded by transport in a river or glacial environment.

Uses & Applications

Used primarily as decorative landscaping stone, drainage aggregate, and in construction as a sturdy base material; sometimes used for lapidary tumbling.

Geological Facts

Quartzite is so strong that when it breaks, it fractures through the quartz grains rather than along the boundaries between them, unlike sandstone.

Field Identification & Locations

Identify in the field by its hardness (cannot be scratched by a steel knife) and smooth, water-worn texture. Commonly found in riverbeds, beaches, and glacial till.

Identified on: 5/4/2026

Mode: Standard