metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (due to iron oxides); Luster: vitreous to dull; Crystal structure: granular/sugary texture; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan (due to iron oxides)
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (due to iron oxides); Luster: vitreous to dull; Crystal structure: granular/sugary texture; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. This specimen appears to be a water-worn river cobble, suggesting more recent transport in a fluvial environment.
Uses & applications
Used extensively in construction as road ballast, railway tracks, and crushed stone. High-purity quartzite is used to produce glass and silicon metal. It is also used as decorative stone in landscaping.
Geological facts
Quartzite is so tough that it often survives intense erosion where other rocks wear away, forming prominent ridges and peaks. It is harder than steel and will easily scratch a glass plate.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a knife) and its grainy, 'sugary' appearance when fractured. It is found globally in mountainous regions or as cobbles in riverbeds. Collectors often look for colorful or banded varieties.
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