metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: White to grey, sometimes yellowish or brownish due to iron; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Fracture: Conchoidal to uneven; Specific Gravity: 2.6-2.65
- Hardness
- 7 on Mohs scale
- Color
- White to grey, sometimes yellowish or brownish due to iron
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to grey, sometimes yellowish or brownish due to iron; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Fracture: Conchoidal to uneven; Specific Gravity: 2.6-2.65
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone under intense heat and pressure, typically during mountain-building events (orogeny). The individual quartz grains recrystallize into an interlocking mosaic.
Uses & applications
Used in construction for road ballast, floor tiles, and roofing. Higher purity varieties are used to produce glass 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 the caps of many mountain ridges. It is frequently mistaken for marble, but unlike marble, it will not fizz when exposed to acid.
Field identification & locations
Identify it by its extreme hardness (it will easily scratch glass) and its grainy, sandpaper-like texture that has been 'fused' together. Unlike sandstone, it breaks through the grains rather than around them. Found globally in ancient mountain belts.
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