metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, though impurities can cause red or pink tints; Luster: vitreous to dull; Crystal structure: interlocking mosaic of quartz grains; Cleavage: none (conchoidal 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, though impurities can cause red or pink tints; Luster: vitreous to dull; Crystal structure: interlocking mosaic of quartz grains; Cleavage: none (conchoidal 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, original quartz grains recrystallize and fuse into a dense, hard rock. Geological age varies globally from Precambrian to more recent tectonic events.
Uses & applications
Used extensively in construction as road ballast, gravel, and dimension stone for flooring and walls. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and glass.
Geological facts
Quartzite is so tough that it often outlasts the mountain ranges it forms, creating resistant ridges and peaks. It is frequently mistaken for marble, but unlike marble, it will not fizz when in contact with acid and is hard enough to scratch glass.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch a steel knife blade) and its granular, sugary appearance on fresh breaks. It is commonly found in folded mountain belts and ancient cratonic shields worldwide.
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