metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale. Color: White, grey, or yellowish. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, exhibits conchoidal or irregular fracture. Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- White, grey, or yellowish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: White, grey, or yellowish. Luster: Vitreous to dull. Crystal structure: Hexagonal (microcrystalline). Cleavage: None, exhibits conchoidal or irregular fracture. Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under extreme heat and pressure. This recrystallization interlocks the quartz grains into a very hard and durable rock mass. They occur in many geological ages but are common in Precambrian and Paleozoic terranes.
Uses & applications
Used widely in construction as crushed stone for road beds, railway ballast, and concrete aggregate. Higher quality pieces are used as decorative stone, countertops, and in flooring.
Geological facts
Quartzite is so tough that it often survives intense erosion better than the rocks surrounding it, forming prominent ridges and mountain peaks. It is frequently mistaken for marble, but can be distinguished by its superior hardness.
Field identification & locations
Identify in the field by its grainy, sandpaper-like texture (though smoother when metamorphosed) and its inability to be scratched by steel. It is commonly found in mountain ranges and areas with ancient continental crust.
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