metamorphic
Quartzite
Quartzite (Primary mineral: SiO2)
Hardness: 7 on Mohs scale; Color: typically white to grey, sometimes reddish or brownish due to iron oxide; Luster: vitreous to dull; Crystal structure: hexagonal (re-crystallized); Cleavage: none, breaks with conchoidal fracture; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to grey, sometimes reddish or brownish due to iron oxide; Luster: vitreous to dull; Crystal structure: hexagonal (re-crystallized); Cleavage: none, breaks with conchoidal fracture; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz sandstone under extreme heat and pressure, typically during mountain-building events (orogeny). The original quartz grains recrystallize and fuse into a dense, interlocking mosaic.
Uses & applications
Used as crushed stone for road construction, railway ballast, and in the manufacturing of glass and ceramics. High-purity quartzite is used to produce ferrosilicon and industrial sand.
Geological facts
Quartzite is so hard that it can scratch steel or glass. On a mountain range, quartzite layers often form the highest ridges because it is significantly more resistant to chemical and physical weathering than the rocks around it.
Field identification & locations
Identify in the field by its grainy texture that looks like sandstone but cannot be scratched by a knife; unlike sandstone, which breaks around grains, quartzite breaks through the grains. Found globally in ancient mountain belts like the Appalachians or the Alps.
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