metamorphic
Quartzite
Quartzite (mostly SiO2)
Hardness: 7 on Mohs scale; Color: white, grey, or yellowish; Luster: vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- white, grey, or yellowish
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: white, grey, or yellowish; Luster: vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and building stone. High-purity quartzite is used to produce glass, silicon metal, and abrasives. In jewelry, it is occasionally used as a gemstone or in beads.
Geological facts
Quartzite is so hard that it will scratch glass and even steel. It is often more resistant to weathering than the surrounding rock, often forming the peaks of ridges and mountains.
Field identification & locations
Identify in the field by its extreme hardness and granular, sugary appearance. Unlike sandstone, when broken, it breaks across the quartz grains rather than around them. Common in metamorphic belts worldwide.
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