metamorphic
Quartzite
Quartzite (consisting primarily of SiO2)
Hardness: 7 on Mohs scale. Color: Gray, white, or light tan with some iron staining. Luster: Vitreous to greasy on fresh surfaces but dull when weathered. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, breaks with conchoidal or splintery fracture.
- Hardness
- 7 on Mohs scale
- Color
- Gray, white, or light tan with some iron staining
- Luster
- Vitreous to greasy on fresh surfaces but dull when weathered
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Physical properties
Hardness: 7 on Mohs scale. Color: Gray, white, or light tan with some iron staining. Luster: Vitreous to greasy on fresh surfaces but dull when weathered. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, breaks with conchoidal or splintery fracture.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse into a dense, interlocking network of crystals.
Uses & applications
Used as crushed stone for road construction and railway ballast. Due to its resistance to weathering and chemicals, it is also used for building facades, floor tiles, and as a source of silica in glass manufacturing.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in mountainous areas, forming prominent ridges and peaks. It is often confused with marble, but can be distinguished because quartzite will scratch glass while marble will not.
Field identification & locations
Identify by its extreme hardness and grainy but sparkly appearance; unlike sandstone, it breaks across grains rather than around them. Found globally in ancient mountain belts and glacial till.
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