metamorphic
Quartzite
Quartzite (Primary mineral: SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-tan to reddish-brown (caused by iron oxide impurities); Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-tan to reddish-brown (caused by iron oxide impurities); Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together into a dense, solid rock. This can occur in various geological ages during mountain-building events.
Uses & applications
Used primarily in construction for road ballast, railway tracks, and decorative building stone. In crushed form, it is used for sandblasting or as an industrial abrasive. Occasionally used as a lapidary material for tumbled stones.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges it was part of, frequently being found as weather-resistant pebbles in riverbeds. It is significantly harder than the sandstone from which it originates.
Field identification & locations
Identify in the field by its grainy, sugary texture and extreme hardness (it will easily scratch glass and steel). Typical locations include the Appalachian Mountains (USA), various parts of the UK, and ancient shields in Brazil and Canada. Pieces are often found as weathered rubble or glacial drift.
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