metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Crystal structure: Hexagonal (trigonal); Cleavage: none, conchoidal fracture; Specific gravity: 2.6-2.7. Highly resistant to chemical and physical weathering.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan; Luster: vitreous to dull; Crystal structure: Hexagonal (trigonal); Cleavage: none, conchoidal fracture; Specific gravity: 2.6-2.7. Highly resistant to chemical and physical weathering.
Formation & geological history
Quartzite is formed when quartz-rich sandstone is subjected to high heat and pressure (metamorphism), usually during tectonic plate collisions. This causes the individual quartz grains to recrystallize and fuse together into a dense, hard rock.
Uses & applications
Used extensively in construction as crushed stone for road bases and railway ballast. It is also used as dimension stone for tiles, countertops, and decorative flooring. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so hard that it will scratch glass and even steel. It is often more resistant to erosion than the surrounding rocks, frequently forming the tops of ridges and mountains. It is sometimes mistaken for marble, but unlike marble, it will not fizz when exposed to acid.
Field identification & locations
Identify in the field by its extreme hardness and its sugary, granular texture where it has been broken. It often has a slight sparkle due to the fused quartz crystals. Commonly found in folded mountain belts globally.
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