metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: white, gray, tan, or yellowish; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none; Specific gravity: approx 2.65.
- Hardness
- 7 on Mohs scale
- Color
- white, gray, tan, or yellowish
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: white, gray, tan, or yellowish; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none; Specific gravity: approx 2.65.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together. It is found in mountain-building belts globally.
Uses & applications
Used in construction as crushed stone for road beds, as dimension stone for counter tops or flooring, and as a raw material in the glass and metallurgy industries.
Geological facts
Quartzite is so tough that it often survives intense weathering better than surrounding rocks, forming the caps of many mountain ranges. It is harder than steel and can scratch glass easily.
Field identification & locations
Identify in the field by its sugary texture and extreme hardness (it will not be scratched by a knife). It breaks across grain boundaries rather than around them, unlike sandstone. Common in Precambrian shields and folded mountain belts.
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