Quartzite Pebble

Physical Properties

Hardness: 7 (Mohs scale); Color: Gray to brownish-tannish; Luster: Dull to waxy; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & Geological History

Formed through the regional metamorphism of quartz sandstone. Under intense heat and pressure, the sand grains recrystallize and fuse together into a dense, hard rock. This specimen shows significant rounding due to fluvial (river) or glacial transport.

Uses & Applications

Used as a ballast in construction, as a decorative stone in landscaping (river rock), and in the manufacture of glass and ceramics due to high silica content.

Geological Facts

Quartzite is so tough that it often survives billions of years of erosion, frequently appearing as smooth, rounded cobbles in stream beds long after the surrounding softer rocks have worn away.

Field Identification & Locations

Identify in the field by its hardness (it will scratch glass) and its lack of reaction to acid. Unlike sandstone, it will break through the grains rather than around them, showing a granular, sugary texture on fresh surfaces.

Identified on: 4/13/2026

Mode: Standard