metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but streaks of pink, red, or yellow occur due to iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (as quartz); Cleavage: None, breaks with conchoidal or irregular fracture; 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 to gray, but streaks of pink, red, or yellow occur due to iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (as quartz); Cleavage: None, breaks with conchoidal or irregular fracture; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, interlocking mosaic of crystals.
Uses & applications
Used primarily in construction for road ballast, railroad ballast, and dimension stone for flooring or wall coverings. Highly pure quartzite is used to produce silica sand for glassmaking and industrial abrasives.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rock, forming prominent ridges and hills. It is often confused with marble, but can be distinguished because quartzite is harder and will not react with acid.
Field identification & locations
Identify in the field by its extreme hardness (it will scratch glass easily) and its sugary, crystalline appearance on fresh surfaces. It is found globally in mountainous regions and ancient shield areas like the Appalachians or the Scottish Highlands.
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