metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 (Mohs scale); Color: White, gray, pink, or reddish-brown due to iron impurities; Luster: Vitreous to dull; Crystal structure: Non-foliated, granoblastic; Cleavage: None, breaks with a conchoidal fracture.
- Hardness
- 7 (Mohs scale)
- Color
- White, gray, pink, or reddish-brown due to iron impurities
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: White, gray, pink, or reddish-brown due to iron impurities; Luster: Vitreous to dull; Crystal structure: Non-foliated, granoblastic; Cleavage: None, breaks with a conchoidal fracture.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone subjected to high heat and pressure, causing original quartz grains to recrystallize and fuse.
Uses & applications
Used in construction as road ballast, gravel, floor tiles, and countertop surfaces. High-purity quartzite is used to produce silica sand for glassmaking and silicon metal.
Geological facts
Quartzite is so durable that it often forms the peaks of mountain ranges because it resists weathering better than surrounding rocks. It is frequently mistaken for marble but is much harder and will not react with acid.
Field identification & locations
Look for a rock that scratches glass easily and has a sugary, crystalline texture on a fresh break. It lacks the layering seen in schist or the bedding planes seen in sandstone. Found worldwide in ancient mountain belts.
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