metamorphic
Quartzite
Metamorphic Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with reddish hues from iron oxides; Luster: vitreous (glassy) to dull; Crystal structure: Trigonal/Hexagonal (largely destroyed by metamorphism); Cleavage: none, fractures conchoidally; Specific Gravity: 2.6–2.7
- Hardness
- 7 on Mohs scale
- Luster
- vitreous (glassy) to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with reddish hues from iron oxides; Luster: vitreous (glassy) to dull; Crystal structure: Trigonal/Hexagonal (largely destroyed by metamorphism); Cleavage: none, fractures conchoidally; Specific Gravity: 2.6–2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse into a dense, interlocking matrix. This process occurs in orogenic (mountain-building) belts globally.
Uses & applications
Used in the construction of roads and railway ballast. High-quality quartzite is used as a source of silica for glass making and metallurgy. Selected pieces are used for kitchen countertops or decorative stone, and smooth river-worn specimens are popular with collectors.
Geological facts
Quartzite is so durable and weather-resistant that it often forms the capstones of mountain ranges. It is significantly harder and more resilient than its parent rock, sandstone. If you break it, the fracture cuts through the sand grains rather than around them.
Field identification & locations
Identify in the field by checking for high hardness (it will scratch glass) and a sugary or crystalline texture. Look for its tendency to break across grains. Commonly found in eroded mountainous areas or as rounded cobbles in riverbeds.
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