metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: Reddish-brown (due to iron oxide impurities); Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 on Mohs scale
- Color
- Reddish-brown (due to iron oxide impurities)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Reddish-brown (due to iron oxide impurities); Luster: Vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the metamorphism of quartz-rich sandstone. Under intense heat and pressure, quartz grains recrystallize and fuse together. The reddish tint suggests the presence of hematite or other iron minerals during formation.
Uses & applications
Used in construction as crushed stone for road ballast, roofing granules, and as a decorative building stone. Highly prized when polished for lapidary work.
Geological facts
Quartzite is so tough that it often survives intense weathering that destroys other rocks, leading to the formation of 'quartzite ridges' in mountain ranges. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Identify in the field by its extreme hardness and sugary, granular texture. Unlike sandstone, quartzite breaks across the quartz grains rather than around them. Common in Precambrian shield areas and folded mountain belts.
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