metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but pink, red, or orange due to iron impurities; Luster: vitreous to dull; Crystal structure: hexagonal (cryptocrystalline in this form); Cleavage: none, breaks with a conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, but pink, red, or orange due to iron impurities; Luster: vitreous to dull; Crystal structure: hexagonal (cryptocrystalline in this form); Cleavage: none, breaks with a conchoidal fracture.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together. It can range from Proterozoic to more recent geological ages depending on the tectonic setting.
Uses & applications
Used in construction as road ballast, railway ballast, and decorative stone. Sometimes used in glass manufacturing if high purity, or as a gemstone if displaying unique patterns.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, creating prominent ridges or hills. It is often confused with marble, but unlike marble, it will not fizz when exposed to acid.
Field identification & locations
Identify by its extreme hardness (it will scratch glass and steel) and its granular, sugary texture. Common in mountain belts where tectonic activity has occurred. Collectors look for pieces with interesting iron-staining patterns.
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