metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 (Mohs scale); Color: White, grey, or greenish-grey; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7.
- Hardness
- 7 (Mohs scale)
- Color
- White, grey, or greenish-grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, grey, or greenish-grey; Luster: Vitreous to dull; Crystal structure: Hexagonal (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, typically during mountain-building events (orogeny). The original quartz sand grains recrystallize into a dense interlocking mosaic.
Uses & applications
Used widely in construction as crushed stone for road grit and railway ballast. Due to its hardness, it is also used for floor tiles, countertops, and as a decorative stone in landscaping.
Geological facts
Quartzite is so hard that it can easily scratch steel; it is often harder than the parent sandstone it originated from. In ancient times, it was occasionally used to make stone tools where flint was unavailable.
Field identification & locations
Identify in the field by its extreme hardness and grainy, sugary texture when freshly broken. Unlike marble, it will not fizz when exposed to acid. Commonly found in folded mountain ranges globally.
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