metamorphic
Quartzite
Quartzite (SiO2 dominant)
Hardness: 7 (Mohs scale); Color: Tan, beige, or yellowish due to iron oxides; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Tan, beige, or yellowish due to iron oxides
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, beige, or yellowish due to iron oxides; Luster: Vitreous to waxy; Crystal structure: Trigonal/Hexagonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together, forming an interlocking structure of quartz crystals.
Uses & applications
Used in construction as crushed stone for road beds, railway ballast, and building stone. 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 other rocks in the field, forming prominent ridges and peaks. It is harder and more durable than the sandstone from which it originated.
Field identification & locations
Identify by its hardness (it will easily scratch glass) and its sugary, crystalline texture. It is commonly found in mountainous regions or ancient shield areas where tectonic plate collisions occurred.
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