metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but often yellow or reddish due to iron oxides; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but often yellow or reddish due to iron oxides; Luster: Vitreous to dull; Crystal structure: Non-foliated, granular; Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during tectonic plate collisions. This specimen shows significant rounding and weathering, suggesting transport by water.
Uses & applications
Used in construction as crushed stone, road ballast, and decorative stone. High-purity quartzite is used to produce silica sand for glassmaking and silicon for electronics.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the tops of ridges and hills, as it resists erosion better than the surrounding rock types. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Identify in the field by its grainy, sugary texture and extreme hardness (it will not be scratched by a steel blade). Commonly found in ancient mountain belts and riverbeds as rounded 'river rocks'.
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