metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: tan, white, or gray; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- tan, white, or gray
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: tan, white, or gray; Luster: vitreous to dull; Crystal structure: hexagonal (microcrystalline); Cleavage: none; 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, causing the quartz grains to recrystallize and fuse together.
Uses & applications
Commonly used in construction for road ballast, floor tiles, and countertop surfaces. High-quality specimens are used in glass-making or as decorative landscaping stones.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, often forming the caps of ridges and mountains. It is harder than steel and will easily scratch glass.
Field identification & locations
Identify in the field by its grainy, sugary appearance and extreme hardness. Unlike limestone, it will not fizz when exposed to acid. Found globally in ancient mountain belts and shield areas.
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