metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-brown to grey (due to iron oxide impurities); Luster: Vitreous to dull; Crystal Structure: Non-foliated, granular; Cleavage: None (breaks with conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown to grey (due to iron oxide impurities)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown to grey (due to iron oxide impurities); Luster: Vitreous to dull; Crystal Structure: Non-foliated, granular; Cleavage: None (breaks with conchoidal fracture).
Formation & geological history
Formed from the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together. Can range from Precambrian to Cenozoic in age.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a decorative stone in architecture or landscaping. High-purity quartzite is used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than along the boundaries between them, unlike its parent rock, sandstone. It is highly resistant to chemical weathering.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of fizzing with acid. Commonly found in folded mountain ranges. Collectors look for smooth, river-worn cobbles like this specimen.
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