metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Gray, white, or light tan; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or light tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Gray, white, or light tan; Luster: Vitreous to dull; Crystal structure: Trigonal (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 into a dense rock. It can date back to various geological eras depending on location.
Uses & applications
Used as crushed stone for road construction, railway ballast, and in the manufacturing of glass and ceramics. High-purity quartzite is used to produce ferrosilicon and industrial silica sand.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, forming prominent ridges and hills. Unlike sandstone, it will break through the quartz grains rather than around them when struck.
Field identification & locations
Identify in the field by its extreme hardness (scratches glass) and its sugary, granular texture that looks like sand but cannot be rubbed off. Commonly found in folded mountain belts and ancient shield regions.
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