metamorphic
Quartzite
Quartzite (mostly SiO2)
Hardness: 7 on Mohs scale; Color: white, gray, yellowish, or reddish; Luster: vitreous to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- white, gray, yellowish, or reddish
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: white, gray, yellowish, or reddish; Luster: vitreous to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogeny).
Uses & applications
Used in construction for road ballast, roofing tiles, and flooring. Highly pure quartzite is used to produce glass and silica products.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, forming prominent ridges and hills. It is often confused with marble but is much harder and won't react with acid.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and its granular, sandpaper-like texture that has been fused into a solid mass. Found in metamorphic belts globally.
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