metamorphic
Quartzite Cobble
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Off-white, tan, with brown staining; Luster: Dull/Waxy; Structure: Granular/Microcrystalline; Extremely durable and resistant to scratching.
- Hardness
- 7 on Mohs scale
- Color
- Off-white, tan, with brown staining
- Luster
- Dull/Waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: Off-white, tan, with brown staining; Luster: Dull/Waxy; Structure: Granular/Microcrystalline; Extremely durable and resistant to scratching.
Formation & geological history
Originally formed as quartz sandstone, this rock underwent intense heat and pressure (metamorphism) which fused the sand grains together. It was then rounded into a sphere-like shape by water erosion in a river or glacial environment.
Uses & applications
Large quartzite cobbles and boulders are used in landscaping, construction aggregate, and as high-silica raw material in manufacturing.
Geological facts
Quartzite is one of the most physically durable and chemically resistant rocks found on Earth's surface. Rounded specimens like this are often mistaken for fossils or eggs due to their symmetrical shape.
Field identification & locations
Identify by its extreme hardness (it will scratch glass and steel) and its granular, sugary appearance when broken. Look for it in riverbeds or glacial till deposits.
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