metamorphic
Quartzite
Quartzite (mostly SiO2)
Hardness: 7 on Mohs scale; Color: Pinkish-tan or light brown; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline aggregate); Cleavage: None (conchoidal fracture); SG: 2.63-2.65
- Hardness
- 7 on Mohs scale
- Color
- Pinkish-tan or light brown
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Pinkish-tan or light brown; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline aggregate); Cleavage: None (conchoidal fracture); SG: 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 individual quartz grains recrystallize into a locked mosaic of crystals.
Uses & applications
Used as a decorative stone in landscaping, crushed stone for road construction, railroad ballast, and sometimes as a building stone or for making floor tiles.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges and peaks of mountain ranges because it resists weathering better than surrounding rocks.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, granular texture. Unlike sandstone, it will break across the grains rather than around them. Found globally in ancient mountain belts.
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