metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, reddish-brown, often with pinkish hues from iron oxidation; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, exhibits conchoidal or irregular fracture; Specific gravity: Approx 2.6
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, reddish-brown, often with pinkish hues from iron oxidation; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, exhibits conchoidal or irregular fracture; Specific gravity: Approx 2.6
Formation & geological history
Formed through the metamorphism of quartz sandstone. Intense heat and pressure cause the individual sand grains to recrystallize and fuse together. This can occur during regional metamorphism at convergent plate boundaries.
Uses & applications
Used primarily in construction for road ballast, building stones, and flooring. In jewelry, it is used for cabochons and decorative carvings. Some high-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so tough that it often survives long after the surrounding rock has been eroded away, frequently forming the tops of ridges and mountains. It is harder than steel and can easily scratch a glass plate.
Field identification & locations
Identify in the field by its extreme hardness and glassy appearance on fresh breaks. Unlike sandstone, quartzite breaks across the sand grains rather than around them. It is commonly found in mountain ranges like the Appalachians or the Alps.
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