metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to grey, but often tinged yellow or brown by iron oxides; Luster: vitreous (glassy); Crystal structure: Trigonal (as microcrystalline quartz); Cleavage: none; Specific gravity: approx. 2.65.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous (glassy)
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to grey, but often tinged yellow or brown by iron oxides; Luster: vitreous (glassy); Crystal structure: Trigonal (as microcrystalline quartz); Cleavage: none; Specific gravity: approx. 2.65.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together, creating a tough, interlocking network of crystals.
Uses & applications
Used as crushed stone for road construction, railroad ballast, and building stone. High-purity quartzite is used to produce glass, ferrosilicon, and silicon metal.
Geological facts
Quartzite is so tough and resistant to chemical weathering that it often forms the ridges and peaks of mountain ranges. It is significantly harder and more durable than the sandstone it originated from.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its grainy, sugary texture. Unlike marble, it will not fizz when exposed to acid. Commonly found in folded mountain belts and ancient cratons.
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