metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White, gray, or tan with iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White, gray, or tan with iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White, gray, or tan with iron staining; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high heat and pressure, quartz grains recrystallize and fuse together into a dense, crystalline rock.
Uses & applications
Used as crushed stone for road construction, railway ballast, and in the manufacturing of glass and ceramics. It is also used as a decorative building stone and for countertops.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of mountains and ridges, as it resists weathering much better than surrounding rocks. It can be distinguished from sandstone because it breaks through the quartz grains rather than around them.
Field identification & locations
Look for a sugary, granular texture that sparkles in sunlight. It is extremely hard and will easily scratch glass. Found globally in ancient mountain belts and riverbeds where it weathered out as cobbles.
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