Quartzite (River Pebble)

Physical Properties

Hardness: 7 (Mohs scale); Color: Tan, brown, or pinkish-gray with white patches; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7

Formation & Geological History

Formed when quartz-rich sandstone is subjected to high heat and pressure, causing the original quartz grains to recrystallize into a dense interlocking mosaic. The rounded shape indicates significant transport and erosion by water (fluvial processes).

Uses & Applications

Aggregates in construction, shoreline stabilization, decorative landscaping, and occasionally as a source of silica for glassmaking. Smooth specimens are popular for meditation stones or decorative crafts.

Geological Facts

Quartzite is so tough that it often survives intense erosion that wears away surrounding softer rocks. It is harder than steel and will scratch a glass plate easily. Many river pebbles like this one were rounded over thousands of years of travel downstream.

Field Identification & Locations

Identify in the field by its hardness (cannot be scratched by a knife), its sugary or grainy texture when broken, and its lack of reaction to acid. Commonly found in riverbeds, glacial deposits, and beaches.

Identified on: 5/4/2026

Mode: Standard