metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, tan, or yellowish-white; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
- Hardness
- 7 on Mohs scale
- Color
- Gray, tan, or yellowish-white
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, tan, or yellowish-white; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing quartz grains to recrystallize and fuse together. Often associated with convergent plate boundaries.
Uses & applications
Used as a decorative stone in construction (countertops, flooring, wall cladding), as railroad ballast, and as a source of silica for glass manufacturing.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges and peaks of mountain ranges because it weathers much more slowly than surrounding rocks.
Field identification & locations
Identify by its extreme hardness (it will scratch glass easily) and its sugary, crystalline texture. Unlike sandstone, it breaks across the grains rather than around them. Found globally in ancient mountain belts.
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