metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white with dark inclusions; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white with dark inclusions
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white with dark inclusions; 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 mountain-building environments (orogenic belts).
Uses & applications
Used as a decorative stone, in construction as crushed stone for roadbeds or railway ballast, and in the manufacturing of glass or ceramics.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks in a landscape, typically forming the peaks of ridges or hills. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness and grainy texture that looks like sand but feels smooth like glass. It breaks across grains rather than around them, unlike sandstone. Common in fold-mountain ranges.
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