metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Off-white, light gray, or tan; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Off-white, light gray, or tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Off-white, light gray, or tan; Luster: Vitreous to dull; Crystal structure: Trigonal (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, causing sand grains to recrystallize into a locked mosaic of quartz crystals. Can range from Proterozoic to more recent geological eras.
Uses & applications
Used in construction as crushed stone for road base or railway ballast, as dimension stone for counter tops and flooring, and as a source of silica for glass manufacturing.
Geological facts
Quartzite is so durable that when it breaks, it fractures through the individual sand grains rather than around them, unlike sandstone. It is often mistake for marble but is much harder and will not react with acid.
Field identification & locations
Identify by its extreme hardness (it will easily scratch glass) and its sugary, crystalline appearance on fresh breaks. Found globally in mountain belts and areas of uplifted metamorphic basement rock.
