metamorphic
Quartzite Cobble
Metamorphosed Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white with subtle banding; Luster: Dull to vitreous; Structure: Granular/crystalline; Cleavage: None; Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white with subtle banding
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white with subtle banding; Luster: Dull to vitreous; Structure: Granular/crystalline; Cleavage: None; Specific Gravity: 2.6-2.7
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure, typically during tectonic plate collisions. This specimen is a water-worn river stone or beach cobble.
Uses & applications
Used as a construction aggregate, for railroad ballast, in glass manufacturing (if high purity), and as decorative landscaping stones.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the capstones of mountain ranges and resists erosion better than most other rocks.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel blade) and its granular, sugary appearance. Commonly found in riverbeds and glacial deposits.
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