metamorphic
Quartzite
Metamorphosed Quartz Sandstone
Hardness: 7 (Mohs scale); Color: Pinkish-red to brownish due to iron oxide impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, breaks with conchoidal fracture.
- Hardness
- 7 (Mohs scale)
- Color
- Pinkish-red to brownish due to iron oxide impurities
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Pinkish-red to brownish due to iron oxide impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None, breaks with conchoidal fracture.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together, creating a hard, dense rock. These specimens can range from Proterozoic to more recent geological eras.
Uses & applications
Used primarily in construction as crushed stone for road ballast or roofing granules. High-purity quartzite is used to produce silica sand for glassmaking and silicon metal. It is also used as a decorative stone in landscaping.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, forming ridges and mountain peaks. Unlike sandstone which breaks around its grains, quartzite breaks through the grains due to the intense fusion during metamorphism.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its grainy, sugary appearance despite being very dense. Commonly found in mountainous regions or as river-worn cobbles in glacial till.
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