metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or tan with possible pink/red hues from iron; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None; Specific Gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, or tan with possible pink/red hues from iron
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or tan with possible pink/red hues from iron; Luster: Vitreous to dull; Crystal structure: Trigonal (granular); Cleavage: None; Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize into a dense, interlocking matrix. Usually found in mountain belts where tectonic plates collide.
Uses & applications
Crushed stone for road construction, railway ballast, building stone, decorative landscaping, and as a source of silica for glass and abrasive manufacturing.
Geological facts
Quartzite is so durable that it often remains as the capstones or ridges of mountains while softer rocks around it erode away. It is often harder than the steel blade of a knife.
Field identification & locations
Identify by its hardness (it will scratch glass) and granular, sugary appearance. It lacks the 'fizz' reaction to acid seen in marble. Commonly found in riverbeds or mountainous regions worldwide.
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