Quartzite pebble

Physical Properties

Hardness: 7 (Mohs scale); Color: Gray to bluish-gray with iron staining; Luster: Vitreous/waxy; Structure: Non-foliated granoblastic; Specific Gravity: 2.6-2.7.

Formation & Geological History

Formed through the metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events (orogeny). This specific piece is a 'river rock' or 'alluvial pebble' that has been water-worn and smoothed in a high-energy environment like a stream or river bed.

Uses & Applications

Commonly used in landscaping, as railroad ballast, in construction as crushed stone, and sometimes as a source of high-purity silica for glassmaking.

Geological Facts

Quartzite is so tough and abrasion-resistant that it often remains as pebbles and boulders long after other rocks have eroded away. It is harder than steel and will scratch glass easily.

Field Identification & Locations

Identify in the field by its extreme hardness (cannot be scratched by a knife) and its sugary or glassy appearance on a fresh break. It is ubiquitous in riverbeds worldwide, particularly in areas with ancient mountain ranges.

Identified on: 4/18/2026

Mode: Standard