metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (often yellowish due to iron oxides); Luster: vitreous (glassy) to dull; Crystal structure: Trigonal (as microcrystalline quartz grains); Cleavage: none, breaks with a conchoidal to irregular fracture; Specific gravity: 2.6 to 2.7.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous (glassy) to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (often yellowish due to iron oxides); Luster: vitreous (glassy) to dull; Crystal structure: Trigonal (as microcrystalline quartz grains); Cleavage: none, breaks with a conchoidal to irregular fracture; Specific gravity: 2.6 to 2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure reciprocal to deep burial or tectonic activity cause the quartz grains to recrystallize and fuse together, creating a hard, dense rock. This specimen appears to be from a Precambrian or Paleozoic formation.
Uses & applications
Used in construction as crushed stone for road beds, railway ballast, and riprap. Also used as dimension stone in tiles, flooring, and decorative wall coverings. High-purity quartzite is a source of silica for glass manufacturing.
Geological facts
Quartzite is so tough that it often forms the ridgetops of mountain ranges because it resists weathering much better than surrounding rocks. Unlike sandstone, which breaks around grains, quartzite breaks through the quartz grains themselves.
Field identification & locations
Identify in the field by its sugary texture on broken surfaces and its extreme hardness (it will easily scratch glass). It lacks the fizz reaction to acid that marble has. Common in the Appalachian Mountains, Lake Superior region, and Brazil.
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