metamorphic
Quartzite
Quartzite (primarily Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale); Color: Tan, beige, white, or yellowish due to iron oxides; Luster: Vitreous to waxy; Structure: Granular or crystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
- Hardness
- 7 (Mohs scale)
- Color
- Tan, beige, white, or yellowish due to iron oxides
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale); Color: Tan, beige, white, or yellowish due to iron oxides; Luster: Vitreous to waxy; Structure: Granular or crystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. High heat and pressure cause quartz grains to recrystallize and fuse into an extremely hard rock. Highly common in tectonic mountain belts of various geological ages.
Uses & applications
Used in construction as crushed stone, road ballast, and for stone facings. Pure varieties are used in glass manufacturing and as a source of silica. Also popular for landscaping and decorative garden stones.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caprock or ridges of mountain ranges because it resists weathering better than surrounding rocks like marble or schist.
Field identification & locations
Identify by its hardness (it will easily scratch glass or steel) and sugary, granular appearance when broken. It is commonly found in riverbeds, glacial tills, or mountain outcrops. Unlike sandstone, it breaks through the grains rather than around them.
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