metamorphic
Quartzite (River Stone)
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-blue with tan/brown iron staining; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.63–2.65.
- Hardness
- 7 on Mohs scale
- Color
- Grayish-blue with tan/brown iron staining
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-blue with tan/brown iron staining; Luster: Vitreous to waxy; Crystal structure: Trigonal (microcrystalline); Cleavage: Conchoidal fracture; Specific gravity: 2.63–2.65.
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, typically in orogenic belts. This specific specimen has been further smoothed and rounded by fluvial processes (water erosion) in a river or beach environment.
Uses & applications
Used in construction as crushed stone or decorative gravel, and occasionally as a gemstone or in lapidary work if it has unique colors. Its hardness makes it ideal for industrial abrasives.
Geological facts
Quartzite is so hard that it will scratch glass and even steel. It is more resistant to weathering than the sandstone from which it originated, often forming the caps of ridges and mountains.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a knife) and its grainy, sugary look on a fresh break. Common in glacial till and riverbeds across North America and Europe.
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