metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Pink, reddish, or grey; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal system (as quartz grains); Texture: Granular, interlocking sugary appearance.
- Hardness
- 7 on Mohs scale
- Color
- Pink, reddish, or grey
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Pink, reddish, or grey; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal system (as quartz grains); Texture: Granular, interlocking sugary appearance.
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism, causing the sand grains to recrystallize and fuse together.
Uses & applications
Used as a decorative stone in construction, countertops, flooring, and railway ballast. Due to high silica content, it is also used in glass manufacturing and industrial abrasives.
Geological facts
Quartzite is so hard and dense that when struck with a hammer, it will break through the quartz grains rather than around them, unlike its parent stone, sandstone.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel) and lack of reaction to acid. Look for a 'sugary' crystalline texture on fresh breaks. Found globally in mountainous regions where tectonic plates have collided.
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