metamorphic
Quartzite (River Pebble)
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: White, cream, or light tan; Luster: Vitreous to dull; Crystal structure: Hexagonal/Trigonal (macro-crystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- White, cream, or light tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, cream, or light tan; Luster: Vitreous to dull; Crystal structure: Hexagonal/Trigonal (macro-crystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together. This specific specimen has been rounded and smoothed by water transport in a river or stream environment.
Uses & applications
Commonly used in construction as crushed stone for roadbeds or concrete. In higher purities, it is used to produce glass, silicon metal, and ferrosilicon. Smooth river pebbles are often used in landscaping and interior design.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming resistant ridges or hills. Unlike sandstone, which breaks around the sand grains, quartzite is so well-fused that it breaks directly through the individual grains.
Field identification & locations
Identify in the field by its hardness (it will easily scratch glass) and lack of reaction to acid. Look for a 'sugary' texture on fresh breaks. It is ubiquitous in river beds and glacial till throughout North America and Europe.
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