metamorphic
Quartzite
SiO2 (Quartzite)
Hardness: 7 on the Mohs scale; Color: Grayish-tan to light brown; Luster: Vitreous to sugary/sandy; Crystal structure: Trigonal (granular interlocking quartz grains); Cleavage: None, breaks with a irregular or conchoidal fracture.
- Hardness
- 7 on the Mohs scale
- Color
- Grayish-tan to light brown
- Luster
- Vitreous to sugary/sandy
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Physical properties
Hardness: 7 on the Mohs scale; Color: Grayish-tan to light brown; Luster: Vitreous to sugary/sandy; Crystal structure: Trigonal (granular interlocking quartz grains); Cleavage: None, breaks with a irregular or conchoidal fracture.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional or contact metamorphism. The quartz grains recrystallize and interlock densely.
Uses & applications
Used extensively in construction as crushed stone, road base, railway ballast, dimension stone for countertops and building facades, and as a source of silica.
Geological facts
Quartzite is extremely durable and resistant to chemical weathering. Unlike sandstone, when quartzite is broken, the fracture cuts through the quartz grains rather than around them.
Field identification & locations
Identified by its hard, sugary surface texture and resistance to scratching by steel. Extremely common in mountain ranges, metamorphic belts, and stream gravels worldwide.
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