metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale (harder than glass); Color: Usually white or gray, but can be pink, yellow, or green due to impurities; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular texture); Specific gravity: 2.6 to 2.7.
- Hardness
- 7 on Mohs scale (harder than glass)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale (harder than glass); Color: Usually white or gray, but can be pink, yellow, or green due to impurities; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular texture); Specific gravity: 2.6 to 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 together, typically occurring during mountain-building events (orogenic processes).
Uses & applications
Used in construction as crushed stone for road ballast, floor tiles, and decorative wall coverings. Because of its hardness, it is also used for making tools and as a source of silica in glass manufacturing.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caprocks of hills and ridges because it resists weather better than the surrounding softer rocks. In the Stone Age, it was sometimes used to make stone tools when flint was unavailable.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its tendency to break through quartz grains rather than around them (unlike sandstone). Commonly found in ancient mountain ranges like the Appalachians or the Alps.
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