metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on the Mohs scale; Color: typically white to gray, often with yellow, brown, or reddish staining from iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (granular/microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
- Hardness
- 7 on the Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on the Mohs scale; Color: typically white to gray, often with yellow, brown, or reddish staining from iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (granular/microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under high heat and pressure, the individual quartz grains recrystallize and fuse together into a dense, crystalline mass. It is found in mountain belts and Precambrian shields globally.
Uses & applications
Used as a decorative stone in architecture (slabs and tiles), as a source of silica for glassmaking, in the chemical industry, and as railroad ballast or road aggregate due to its durability.
Geological facts
Quartzite is so tough that it often survives intense erosion better than most other rocks, frequently forming the rugged caps of ridges and mountains. It is more durable and chemically resistant than marble, with which it is sometimes confused.
Field identification & locations
Identify in the field by its extreme hardness (it will easily scratch glass) and its granular, sugary texture. Unlike sandstone, quartzite breaks across the grains rather than around them. It is commonly found in riverbeds or near mountain ranges with tectonic history.
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