metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White, gray, or pale green; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- White, gray, or pale green
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White, gray, or pale green; Luster: Vitreous to dull; Crystal structure: Hexagonal (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 together, typically in orogenic belts during mountain-building events.
Uses & applications
Used as a decorative stone in construction, for railway ballast, as a source for silica in glass manufacturing, and as high-durability countertops.
Geological facts
Quartzite is so tough that it often outlasts the surrounding softer rocks, forming prominent ridges and hills. It is often confused with marble, but unlike marble, it will not fizz with acid and is much harder.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it will easily scratch glass). Look for it in glaciated regions or areas with ancient mountain roots. It breaks through the grains rather than around them.
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