metamorphic
Quartzite River Rock
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: light gray, tan, and white with some iron staining; Luster: dull to vitreous; Crystal structure: crystalline/granular; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- light gray, tan, and white with some iron staining
- Luster
- dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: light gray, tan, and white with some iron staining; Luster: dull to vitreous; Crystal structure: crystalline/granular; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed from quartz-rich sandstone subjected to extreme heat and pressure (metamorphism). This specific specimen has been further shaped into a smooth, oval cobble by transport in a river or glacier over thousands of years.
Uses & applications
Used primarily as decorative landscaping stone, drainage material, or aggregate in heavy construction. High-purity quartzite is used as a source of silica for glass and ceramics.
Geological facts
Quartzite is so hard that it will scratch glass and steel. Unlike marble, which it sometimes resembles, it will not fizz when exposed to acid. It is one of the most durable and weather-resistant rocks on Earth's surface.
Field identification & locations
Identify by its extreme hardness and granular 'sugary' texture seen on fresh breaks. This specimen is a typical 'river cobble.' It is found globally in riverbeds, glacial tills, and ancient mountain belts.
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