metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: Grayish-white, translucent to opaque; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Grayish-white, translucent to opaque
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Grayish-white, translucent to opaque; Luster: Vitreous to dull; Crystal structure: Non-foliated, interlocking quartz grains; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. High heat and pressure compressed the original sand grains, causing them to recrystallize into a dense, interlocking mosaic of quartz crystals. Found in mountain belts and metabolic shields.
Uses & applications
Used widely in construction for railway ballast, road aggregate, and floor tiles. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal. It is also used as a decorative stone.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, creating prominent ridges or hills. It can be distinguished from its parent sandstone because it breaks through the grains rather than around them.
Field identification & locations
Look for a very hard, sugary-looking rock that scratches glass and steel. It often has a grainy texture but a glass-like luster on fresh breaks. Very common in old mountain ranges like the Appalachians or the Alps.
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