metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white with sugary texture; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white with sugary texture
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white with sugary texture; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse into a dense, interlocking mosaic. Most common in Precambrian or Paleozoic formations.
Uses & applications
Used heavily in construction as crushed stone for road ballast, roofing granules, and as a decorative building stone. High-purity quartzite is also used to produce silica sand for glass manufacturing and silicon metal.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming high ridges or resistant hills. Unlike sandstone, which breaks around its grains, quartzite breaks straight through the grains due to its high level of fusion.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and its granular, sugary appearance. It is found globally in mountainous regions where tectonic activity has occurred. Collectors look for pieces with interesting mineral inclusions or vibrant colors.
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