metamorphic
Yellow Quartzite (River Pebble)
Quartzite (primarily Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale); Color: Pale yellow to tan; Luster: Vitreous to waxy (when polished/worn); Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: Approx 2.65
- Hardness
- 7 (Mohs scale)
- Color
- Pale yellow to tan
- Luster
- Vitreous to waxy (when polished/worn)
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Physical properties
Hardness: 7 (Mohs scale); Color: Pale yellow to tan; Luster: Vitreous to waxy (when polished/worn); Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: Approx 2.65
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure. It has been further smoothed and rounded by river or alluvial transport, which removed sharp edges and deposited it as a pebble.
Uses & applications
Used in landscaping, decorative gravel, and occasionally as a low-cost gemstone when tumbled. Industrial uses of crushed quartzite include glass making and as a high-strength construction aggregate.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the cap-rock of mountains. In some cases, it can be 99% pure quartz. The yellow tint is usually caused by iron oxide staining (limonite) within the micro-cracks or grain boundaries of the rock.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its grainy, sandpaper-like texture (hidden by its worn surface here). It will not fizz with acid. Found globally in riverbeds and glacial deposits.
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