metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with tan or yellowish staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.63–2.65
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with tan or yellowish staining; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.63–2.65
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, causing the original quartz grains to recrystallize into an interlocking mosaic of crystals.
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction, as railroad ballast, and occasionally for high-silica industrial applications.
Geological facts
Quartzite is so tough and abrasion-resistant that it typically breaks through the quartz grains rather than along the boundaries between them, unlike its parent rock sandstone.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, crystalline surface texture. It is extremely common in ancient mountain ranges and glacial deposits.
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