metamorphic
Quartzite Cobble
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Rusty orange to tan (due to iron oxide staining); Luster: Dull to vitreous; Structure: Massive, non-foliated; Cleavage: None, breaks with conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Color
- Rusty orange to tan (due to iron oxide staining)
- Luster
- Dull to vitreous
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Physical properties
Hardness: 7 on Mohs scale; Color: Rusty orange to tan (due to iron oxide staining); Luster: Dull to vitreous; Structure: Massive, non-foliated; Cleavage: None, breaks with conchoidal fracture.
Formation & geological history
Formed when quartz-rich sandstone is subjected to heat, pressure, and chemical activity of metamorphism. This specific specimen has been rounded by fluvial processes (river transport) and stained by iron-rich groundwater.
Uses & applications
Used in construction as crushed stone for road ballast, as a decorative garden stone, and in high concentrations as a source of silica for glass making.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the ridges and peaks in mountain ranges. It is tougher than the parent sandstone from which it originated.
Field identification & locations
Identify by its extreme hardness (it will easily scratch glass) and lack of visible grains compared to sandstone. Commonly found in riverbeds, glacial tills, and mountainous regions.
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