metamorphic
Quartzite
Quartzite (mostly SiO2)
Hardness: 7 on Mohs scale; Color: white, gray, or greenish-gray; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- white, gray, or greenish-gray
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: white, gray, or greenish-gray; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal; Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7.
Formation & geological history
Formed from the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse together, typically in orogenic belts.
Uses & applications
Used extensively in the construction industry as crushed stone for road ballast, building material, and decorative landscaping stone. High-purity quartzite is used to produce glass and silicon metal.
Geological facts
Quartzite is so tough that it often outlasts the rocks surrounding it, forming prominent ridges and peaks in mountain ranges. It is harder than steel and will scratch glass easily.
Field identification & locations
Identify in the field by its extreme hardness and tendency to break through quartz grains rather than around them (unlike sandstone). Found in mountain ranges and ancient shield areas worldwide.
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