metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray/tan with reddish iron staining; Luster: vitreous to dull; Crystal structure: trigonal (granular); Cleavage: none, breaks with a conchoidal fracture.
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray/tan with reddish iron staining
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray/tan with reddish iron staining; Luster: vitreous to dull; Crystal structure: trigonal (granular); Cleavage: none, breaks with a conchoidal fracture.
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, causing the original quartz grains to recrystallize into an interlocking mosaic. Found in orogenic belts worldwide.
Uses & applications
Commonly used in construction as crushed stone, road ballast, or decorative stone. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caps of ridges and mountains because it resists erosion much better than surrounding rocks.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and its grainy, sugary texture that resembles sandstone but breaks through the grains rather than around them.
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