metamorphic
Quartzite
Metamorphosed Quartz Sandstone (SiO2)
Hardness: 7 on Mohs scale; Color: Whitish to yellowish-tan; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Whitish to yellowish-tan
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Whitish to yellowish-tan; Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific gravity: 2.6-2.7
Formation & geological history
Formed when quartz-rich sandstone is subjected to high heat and pressure during regional metamorphism. This recrystallizes the sand grains into an interlocking mosaic of quartz crystals. Found in folded mountain belts and ancient shield areas.
Uses & applications
Used as crushed stone for road construction and railway ballast. High-purity quartzite is used to produce glass, ferrosilicon, and silicon metal. It is also used as decorative building stone.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than along the grain boundaries as sandstone does. It is often more resistant to weathering than the surrounding rock, frequently forming ridges and hilltops.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass and steel) and its crystalline, sugary appearance. Found in mountain ranges and areas of tectonic activity. Look for a lack of visible cement between grains compared to sandstone.
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