metamorphic
Quartzite Pebble
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-brown to tan (iron staining); Luster: Vitreous to dull; Crystal Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.65
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown to tan (iron staining)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown to tan (iron staining); Luster: Vitreous to dull; Crystal Structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 - 2.65
Formation & geological history
Formed from quartz-rich sandstone subjected to intense heat and pressure (metamorphism), which fuses individual sand grains together into a solid crystalline rock.
Uses & applications
Used primarily as construction aggregate, railway ballast, and decorative garden stone. Pure quartzite is also used to produce silica sand for glassmaking.
Geological facts
Quartzite is so tough that it often outlasts other rocks around it, appearing as resistant ridges or rounded river pebbles like this one. It is harder than steel and can easily scratch glass.
Field identification & locations
Identify in the field by its hardness (cannot be scratched by a knife) and sugary/crystalline appearance on a fresh break. Commonly found in riverbeds, glacial deposits, and mountain ranges.
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