metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but iron impurities often create red, pink, or brownish hues as seen here; Luster: vitreous to dull; Crystal Structure: Tridymite/Quartz; 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: typically white to gray, but iron impurities often create red, pink, or brownish hues as seen here; Luster: vitreous to dull; Crystal Structure: Tridymite/Quartz; 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 from tectonic activity cause the individual quartz grains to recrystallize and fuse together into a dense, interlocking mosaic of crystals.
Uses & applications
Extensively used as crushed stone in road construction, railroad ballast, and building stone. High-purity quartzite is used in the manufacture of glass, silicon metal, and ferrosilicon.
Geological facts
Quartzite is so durable that it often remains as ridges or peaks even after softer surrounding rocks have eroded away. It is tougher than the sandstone from which it originated, meaning it typically breaks through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its hardness (will easily scratch glass) and its sugary, crystalline surface texture. Unlike sandstone, when broken, the fracture surface will cut through the constituent sand grains rather than around them.
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