metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (as seen in image); Luster: vitreous to waxy; Crystal structure: Non-foliated, granular; Cleavage: none (conchoidal or irregular fracture); Specific gravity: 2.6 - 2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically white, gray, or tan (as seen in image)
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan (as seen in image); Luster: vitreous to waxy; Crystal structure: Non-foliated, granular; Cleavage: none (conchoidal or irregular fracture); Specific gravity: 2.6 - 2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartzose sandstone. Under high heat and pressure, the individual quartz grains recrystallize into a dense, interlocking mosaic. Most specimens are from the Proterozoic or Paleozoic eras.
Uses & applications
Used extensively in construction as crushed stone for road beds, railway ballast, and roofing granules. Exceptional pieces are used as dimension stone for wall cladding and floors. High-purity quartzite is used to produce ferrosilicon and industrial silica sand.
Geological facts
Quartzite is so tough that unlike sandstone, where it breaks around the sand grains, quartzite will break through the grains. It is often more resistant to weathering than the surrounding rock, often forming the peaks of ridges and mountains.
Field identification & locations
Identify in the field by its superior hardness (it will easily scratch glass) and its sugary, granular texture on fresh surfaces. Often found in mountainous regions or as river-tumbled 'river jacks' as seen in the background of the image. It will not fizz when exposed to acid (unlike marble).
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