metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, may appear yellowish or reddish due to iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: missing (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, may appear yellowish or reddish due to iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: missing (breaks with conchoidal or irregular fracture); Specific gravity: 2.6 - 2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under high heat and pressure, the individual quartz grains recrystallize and fuse into a dense, interlocking mosaic of crystals. It is found in mountain-building regions globally.
Uses & applications
Used widely in construction as crushed stone for road ballast, floor tiles, roofing, and wall coverings. High-purity quartzite is used to produce glass, ferrosilicon, and silicon metal. It is also a popular decorative stone for countertops.
Geological facts
Quartzite is so tough that it often survives intense erosion to form the peaks of mountain ranges. It is frequently confused with white marble, but unlike marble, quartzite will not react with acid and is hard enough to scratch glass easily.
Field identification & locations
Identify in the field by its grainy, sandpaper-like texture (inherited from sandstone) but extreme hardness. It won't be scratched by a steel blade. Common in ancient metamorphic belts in Canada, Brazil, and the United States (Appalachian and Rocky Mountains).
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