metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically grayish-white but can be reddish-brown due to iron impurities; Luster: vitreous to dull; Structure: granoblastic/interlocking crystalline grain pattern; Cleavage: none.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
Identified More metamorphic →
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Physical properties
Hardness: 7 on Mohs scale; Color: typically grayish-white but can be reddish-brown due to iron impurities; Luster: vitreous to dull; Structure: granoblastic/interlocking crystalline grain pattern; Cleavage: none.
Formation & geological history
Formed from the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together, creating an extremely durable rock.
Uses & applications
Used as crushed stone for road construction, railway ballast, and decorative landscaping. High-purity quartzite is used to produce silica sand for glassmaking and silicon metal.
Geological facts
Quartzite is so tough that it often survives intense weathering that wears away surrounding rocks, often forming the tops of ridges and resistant hills.
Field identification & locations
Identified in the field by its extreme hardness (cannot be scratched by steel) and the way it breaks through its constituent quartz grains rather than around them. Found globally in ancient mountain belts.
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