metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: White to grey, sometimes reddish or brownish due to iron; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White to grey, sometimes reddish or brownish due to iron
- Luster
- Vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: White to grey, sometimes reddish or brownish due to iron; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse into an extremely hard rock. It can form in mountain-building events (orogenic belts).
Uses & applications
Used as crushed stone for road construction and railway ballast. Also used as dimension stone in architecture (countertops, flooring, wall cladding) and as a source of silica for glass and silicon metal production.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the resistant ridges and hilltops in mountain ranges. It was used in prehistoric times to make stone tools when flint was unavailable.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. It breaks across grains rather than around them. Found globally where ancient sandstone beds have undergone metamorphism.
