Quartzite pebble

Physical Properties

Hardness: 7 (Mohs); Color: Pale orange to cream; Luster: Vitreous to waxy (especially when water-worn); Crystal structure: Trigonal (microcrystalline masses); Cleavage: None, conchoidal fracture; Specific gravity: 2.65

Formation & Geological History

Formed through the metamorphism of quartz sandstone under high heat and pressure, which causes the sand grains to recrystallize and fuse together. This specific specimen has been rounded and smoothed by water transport (alluvial/beach action).

Uses & Applications

Used in construction as crushed stone or landscaping gravel. High-purity quartzite is used to produce silica sand for glassmaking and silicon for electronics.

Geological Facts

Quartzite is so tough that it often outlasts the mountain ranges it was formed in, appearing as residual caprock or river cobbles. It will scratch glass easily, unlike similar-looking calcite or gypsum.

Field Identification & Locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and the way it breaks through sand grains rather than around them. Found globally in ancient riverbeds, glacial deposits, and mountain belts.

Identified on: 4/22/2026

Mode: Standard