River Cobble (likely Quartzite or Chert)

Physical Properties

Hardness: 7 on Mohs scale; Color: Brown, tan, and reddish-orange; Luster: Dull to waxy; Structure: Microcrystalline; Specific Gravity: Approx 2.65.

Formation & Geological History

Formed through the regional metamorphism of quartz-rich sandstone or the deposition of silica-rich sediments. The rounded shape indicates extensive transport and erosion by water in a high-energy river or beach environment.

Uses & Applications

Used primarily as decorative landscaping stone, drainage aggregate, and in construction; can be polished for lapidary art.

Geological Facts

River cobbles like this one often travel hundreds of miles from their source, becoming smoother and rounder as they knock against other stones in moving water. Traces of iron oxides give this specimen its reddish-brown tint.

Field Identification & Locations

Identify in the field by its smooth, water-worn surface and extreme hardness (will scratch glass). Commonly found in dry creek beds, river banks, and glacial deposits.

Identified on: 4/30/2026

Mode: Standard