Quartzite River Cobble

Physical Properties

Hardness: 7 on Mohs scale; Color: Tan, brown, and reddish-orange due to iron staining; Luster: Dull/earthy (weathered surface) to vitreous (fresh break); Crystal structure: Granular, interlocking quartz grains; Specific Gravity: 2.6-2.7

Formation & Geological History

Originally formed as quartz sandstone in a sedimentary environment, later subjected to high heat and pressure (metamorphism) that fused the sand grains together. This specific specimen has been rounded and smoothed by water transport in a river or glacial environment.

Uses & Applications

Commonly used in crushed stone for road construction, railway ballast, and as decorative landscaping stones. Highly durable for outdoor use.

Geological Facts

Quartzite is so tough that it often breaks through the individual quartz grains rather than around them, which distinguishes it from sandstone. This specimen likely traveled many miles in a riverbed to achieve its smooth, rounded shape.

Field Identification & Locations

Identify in the field by its hardness (it will easily scratch glass) and its smooth, water-worn texture. It is a common find in riverbeds, gravel pits, and ancient glacial deposits globally.

Identified on: 4/25/2026

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