metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Tan, brown, or grayish
- Luster
- Vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish; Luster: Vitreous to dull; Crystal structure: Trigonal (granular texture); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz sandstone under intense heat and pressure, typically during mountain-building events. The individual quartz grains recrystallize into locked mosaic patterns.
Uses & applications
Used widely in construction for railway ballast, road aggregate, and floor tiles. High-purity quartzite is used to produce silica sand for glass making.
Geological facts
Quartzite is so durable that it can survive long-term erosion better than almost any other rock, often forming the peaks of rugged mountain ranges. It is harder than steel and can easily scratch a glass plate.
Field identification & locations
Identify by its ability to scratch glass and its granular, sugary appearance when broken. Unlike sandstone, it will break through the quartz grains rather than around them. Common in metamorphic belts worldwide.
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