metamorphic
Quartzite
Quartzite (mostly SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white with a slightly green tint; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None, breaks with a conchoidal or uneven fracture.
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white with a slightly green tint
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white with a slightly green tint; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (microcrystalline); Cleavage: None, breaks with a conchoidal or uneven fracture.
Formation & geological history
Formed through the metamorphism of quartz sandstone under high heat and pressure, where individual quartz grains recrystallize into a dense, interlocking mosaic of crystals.
Uses & applications
Used in construction for road ballast, floor tiles, and countertop surfaces. Also used as a source of silica for glass manufacturing and as decorative stone.
Geological facts
Quartzite is so hard and durable that it often outlasts the surrounding rock in mountain ranges, forming prominent peaks and ridges. It is often confused with marble but can be distinguished by its superior hardness.
Field identification & locations
Identified in the field by its hardness (cannot be scratched by a steel knife) and its grainy, sugary appearance on fresh surfaces. Common in metamorphosed mountain belts worldwide.
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