metamorphic
Quartzite
Quartzite (principally SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray but often reddish/brown due to iron oxide; Luster: vitreous to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.6-2.7
- 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 white to gray but often reddish/brown due to iron oxide; Luster: vitreous to dull; Crystal Structure: Trigonal (microcrystalline); Cleavage: None/Conchoidal fracture; Specific Gravity: 2.6-2.7
Formation & geological history
Formed from the metamorphism of quartz sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, creating a very hard, dense rock.
Uses & applications
Used in construction for road ballast, floor tiles, and countertop slabs. High-purity quartzite is used in glassmaking and as a source of silica.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, frequently forming the tops of ridges and mountains. It will scratch glass easily.
Field identification & locations
Identify by its sugary texture and extreme hardness (cannot be scratched by a steel knife). Unlike sandstone, when fractured, quartzite breaks through the quartz grains rather than around them.
