metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be pink or red due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); 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, but can be pink or red due to iron oxides; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.
Formation & geological history
Quartzite is formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism. This process recrystallizes the quartz grains, locking them together into a dense, hard mosaic rock. It is often found in folded mountain belts.
Uses & applications
Used as a decorative stone in construction (crushed stone, flooring, wall coverings), as a source of silica for glass manufacturing, and as a component in metallurgy.
Geological facts
Quartzite is so hard that it can scratch steel. Because it is highly resistant to chemical weathering, it often forms the ridges and peaks of mountain ranges, where it remains long after softer rocks have eroded away.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a knife) and its grainy, sandpaper-like texture that doesn't rub off. Unlike marble, it will not fizz when exposed to acid. Found globally in ancient shield areas and Appalachian-style mountain ranges.
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