metamorphic
Quartzite Cobble
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-tan (appears purple due to lighting); Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Grayish-tan (appears purple due to lighting)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-tan (appears purple due to lighting); Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone through heat and pressure, typically in orogenic belts. This specific specimen is weather-worn and rounded by water transport in a river or coastal environment.
Uses & applications
Used in construction as crushed stone, road ballast, and decorative landscaping. High-purity quartzite is used to produce glass and industrial silica.
Geological facts
Quartzite is so hard that it will scratch glass and even steel. It is more resistant to weathering than the sandstone it originated from, often forming the caps of ridges and mountains.
Field identification & locations
Identify by its extreme hardness and granular, sugary texture. Unlike sandstone, quartzite breaks across the quartz grains rather than around them. Commonly found in riverbeds and glacial tills.
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