metamorphic
Quartzite
Metamorphosed Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: tan, yellow, gray, or reddish due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- tan, yellow, gray, or reddish due to iron oxides
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, yellow, gray, or reddish due to iron oxides; 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. High heat and pressure reciprocal to tectonic compression cause quartz grains to recrystallize and fuse together. It can be found in mountain belts globally, often dating back to the Proterozoic or Paleozoic eras.
Uses & applications
Used extensively as crushed stone for road construction and railway ballast. Due to its durability, it is used for countertops, floor tiles, and as a raw material for silicon production in the glass and electronics industries.
Geological facts
Quartzite is so durable that it often remains as high ridges or peaks on mountains because it resists weathering better than the surrounding rock. It is often mistaken for marble but can be distinguished because quartzite will not react to acid.
Field identification & locations
Identify in the field by its extreme hardness (it will scratch glass) and lack of reaction to dilute hydrochloric acid. It often has a 'sugary' texture on fresh breaks. It is ubiquitous in riverbeds and mountainous glacial deposits.
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