metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, or tan with a sugary texture; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular); Cleavage: None; Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, or tan with a sugary texture
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, or tan with a sugary texture; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular); Cleavage: None; Specific gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz-rich sandstone under high heat and pressure. The original sand grains recrystallize into a locked interlocking mosaic of quartz crystals.
Uses & applications
Used in construction as road ballast, roofing granules, and dimension stone. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal.
Geological facts
Quartzite is so tough that it often breaks through the constituent quartz grains rather than around them. It is one of the most chemically resistant and physically durable rocks on Earth's surface.
Field identification & locations
Identify in the field by its hardness (will scratch glass) and its granular, crystalline appearance that looks like 'sugary' fused sand. It is extremely common in mountain ranges and as river cobbles due to its durability.
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