metamorphic
Quartzite
Silica (SiO2)
Hardness: 7 on Mohs scale; Color: White to light tan/orange; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular); Cleavage: None; Specific gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- White to light tan/orange
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: White to light tan/orange; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (granular); Cleavage: None; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together, creating a much harder and denser rock than the parent sandstone.
Uses & applications
Used in construction for road ballast, flooring, and wall coverings. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal. It is also used as a decorative stone in landscaping.
Geological facts
Quartzite is so tough that it often survives intense weathering that wears away softer rocks, frequently forming the tops of ridges and mountains. It is harder than a steel knife and will easily scratch glass.
Field identification & locations
Identify in the field by its sugary, granular texture and extreme hardness (cannot be scratched by steel). It is commonly found in fold mountain belts globally. Collectors should look for unique colors caused by mineral impurities like hematite.
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