metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White to grey, often with reddish or yellowish tint from impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to grey, often with reddish or yellowish tint from impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together into a dense, interlocking mosaic. Formation can occur across various geological ages including the Precambrian and Paleozoic.
Uses & applications
Used as a decorative stone in architecture, a source of silica for glass manufacturing, railway ballast, and in the production of silicon-based microchips. High-quality varieties are used for countertops and flooring.
Geological facts
Quartzite is so hard that it will scratch glass. It is often confused with marble, but marble is carbonate-based and will fizz in contact with acid, whereas quartzite will not react. Some of the world's most durable mountain peaks are made of quartzite due to its resistance to erosion.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary texture. It is commonly found in fold mountain belts globally. Collectors should look for unique coloration or unusual crystalline impurities.
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