metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White, grey, or pinkish due to iron oxide impurities; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Specific Gravity: 2.6-2.7. It is extremely durable and scratch-resistant.
- Hardness
- 7 (Mohs scale)
- Color
- White, grey, or pinkish due to iron oxide impurities
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, grey, or pinkish due to iron oxide impurities; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Specific Gravity: 2.6-2.7. It is extremely durable and scratch-resistant.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, erasing the original sedimentary structures. It occurs in mountain belts globally, often dating back to the Proterozoic or Paleozoic eras.
Uses & applications
Used widely as crushed stone for road construction and railway ballast. Due to its hardness, it is also used for building facades, floor tiles, and more recently as kitchen countertops (often marketed as 'natural quartzite').
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than along the boundaries between them, unlike its parent rock sandstone. It is often confused with marble, but can be distinguished by its inability to be scratched by a steel blade.
Field identification & locations
To identify in the field, look for a rock that can scratch glass and shows a sugary, crystalline texture that lacks the layers seen in sandstone. It is ubiquitous in glacial drift and riverbeds in many parts of the world.
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