metamorphic
Quartzite
Metamorphosed Sandstone (SiO2)
Hardness: 7 (Mohs scale); Color: Yellow-tan to orange-brown due to iron staining; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
- Hardness
- 7 (Mohs scale)
- Color
- Yellow-tan to orange-brown due to iron staining
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Yellow-tan to orange-brown due to iron staining; Luster: Vitreous to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the individual sand grains and silica cement to recrystallize into a locked mosaic of quartz crystals. They are found in mountain belts and fold systems globally.
Uses & applications
Used as a decorative stone in construction, counter tops, flooring, railway ballast, and crushed stone for road base. Because of its hardness, it is also used as an abrasive.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, forming ridges and mountain peaks. It will scratch glass easily, which helps distinguish it from softer rocks like calcite-bearing marble.
Field identification & locations
Identify by its extreme hardness, grainy texture that looks like boiled sugar, and the way it breaks through the sand grains rather than around them. Commonly found in areas with ancient seafloor deposits that have undergone tectonic uplift.
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