metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or tan staining from iron oxides; Luster: vitreous to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.63-2.65.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with yellow or tan staining from iron oxides; Luster: vitreous to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.63-2.65.
Formation & geological history
Formed through the metamorphism of quartz sandstone. Intense heat and pressure cause the individual quartz grains to recrystallize and fuse together, creating a hard, interlocking mosaic of quartz crystals. Most quartzite dates back to the Proterozoic or Paleozoic eras.
Uses & applications
Used extensively in construction as road ballast, gravel, and building stone. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal. It is also used as a decorative stone in landscaping.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than around them, which distinguishes it from sandstone. Some varieties, like aventurine, are used as gemstones due to mica inclusions.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its sugary, crystalline texture. It is commonly found in folded mountain belts globally, such as the Appalachian Mountains or the Alps.
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