metamorphic
Quartzite
Quartzite (primarily Silicon Dioxide, SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellowish or brownish iron staining; Luster: Vitreous to waxy; Structure: Crystalline/Granular; Cleavage: None (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellowish or brownish iron staining; Luster: Vitreous to waxy; Structure: Crystalline/Granular; Cleavage: None (conchoidal fracture).
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the original sand grains to recrystallize and fuse together. It can be found in mountain ranges and ancient continental shields.
Uses & applications
Used as crushed stone for road construction, railway ballast, and as a decorative stone in architecture. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, forming the peaks of ridges and mountains. It is harder than steel and will easily scratch a glass plate or a knife blade.
Field identification & locations
Identify in the field by its extreme hardness and the way it breaks across grain boundaries rather than around them. It is commonly found in riverbeds as rounded cobbles or in massive outcrops in metamorphic terrains.
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