metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Pinkish-red to grey; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal crystals within a granular mass; Cleavage: None; Specific gravity: 2.63-2.65
- Hardness
- 7 on Mohs scale
- Color
- Pinkish-red to grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Pinkish-red to grey; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal crystals within a granular mass; Cleavage: None; Specific gravity: 2.63-2.65
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, typically during mountain-building events. The original quartz grains recrystallize into a dense interlaced structure.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a decorative stone in landscaping. High-purity quartzite is used to produce ferrosilicon and industrial silica sand.
Geological facts
Quartzite is so tough that it often breaks through the quartz grains rather than along their boundaries, unlike sandstone. It is highly resistant to chemical weathering.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It is commonly found in folded mountain belts and ancient shield areas. Collectors look for unique colors caused by mineral impurities.
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