metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white with translucent areas; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white with translucent areas
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white with translucent areas; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); 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 sand grains to recrystallize and fuse together. These structures can range from Precambrian to relatively recent geological eras.
Uses & applications
Used in construction as crushed stone for road beds, in the chemical industry for silica production, as a decorative building stone (countertops/floor tiles), and occasionally in jewelry as a substitute for more expensive stones.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock in mountain ranges, forming the caps of ridges. Unlike sandstone, when quartzite is broken, it fractures through the sand grains rather than around them.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its granular, sugary texture. It is extremely common in mountainous regions worldwide particularly in the Appalachian Mountains and the Brazilian Highlands.
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