metamorphic
Quartzite Pebbles
Metamorphosed Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Off-white, tan, and reddish-brown due to iron impurities; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None, exhibits conchoidal fracture under the weathered surface.
- Hardness
- 7 on Mohs scale
- Color
- Off-white, tan, and reddish-brown due to iron impurities
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Off-white, tan, and reddish-brown due to iron impurities; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None, exhibits conchoidal fracture under the weathered surface.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together. The rounded shape indicates erosion by water in a river or coastal environment.
Uses & applications
Commonly used in landscaping, as decorative stones, in construction as aggregate, and sometimes in glassmaking if the silica content is exceptionally high.
Geological facts
Quartzite is so tough that it often survives millennia of erosion that wears down surrounding softer rocks. It can be distinguished from sandstone because it breaks across the sand grains rather than around them.
Field identification & locations
Identify by its ability to scratch glass and its grainy, sugary texture under a loupe. It will not react with acid, unlike marble. Found globally in riverbeds and ancient metamorphic belts.
