metamorphic
Quartzite
Metamorphosed Sandstone (SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or pinkish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Granular texture.
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, or pinkish
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or pinkish; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Granular texture.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under extreme heat and pressure, typically during mountain-building events (orogenic processes). The grains of quartz recrystallize and fuse together.
Uses & applications
Used in construction for crushed stone, railway ballast, and decorative stones. High-purity quartzite is used in the glass industry and to produce silicon metal or ferrosilicon.
Geological facts
Quartzite is so tough that it often outlasts other rocks in the field, forming prominent ridges and hills. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify by its hardness (cannot be scratched by a knife) and its grainy, sugary appearance despite being very dense. Found globally in ancient mountain belts like the Appalachians or the Alps.
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