metamorphic
Quartzite Pebble
Metamorphic Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, beige, or white with iron staining; Luster: Vitreous to dull (waxy when polished); Crystal Structure: Hexagonal (trigonal); Grainy texture; No cleavage; Specific gravity: approx. 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, or white with iron staining
- Luster
- Vitreous to dull (waxy when polished)
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, beige, or white with iron staining; Luster: Vitreous to dull (waxy when polished); Crystal Structure: Hexagonal (trigonal); Grainy texture; No cleavage; Specific gravity: approx. 2.65.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under heat and pressure. This specific specimen has been further shaped by fluvial (river) or coastal erosion, resulting in its smooth, rounded 'river stone' shape.
Uses & applications
Used in landscaping, construction aggregate, aquarium decor, and sometimes as a source of high-purity silica for glassmaking. Smooth tumbled versions are common in decorative rock gardens.
Geological facts
Quartzite is so durable that it can survive long-distance transport in rivers and high-energy coastal environments while other rocks wear away. It is often harder than the steel of a knife, a common field test.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and the grainy, sugary appearance of its interior which differentiates it from the microcrystalline texture of chert. Look for it in riverbeds and glacial deposits.
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