metamorphic
Quartzite
Quartzite (SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with brownish or reddish tints from iron impurities; Luster: vitreous to dull; Crystal structure: hexagonal (as quartz); Cleavage: none, breaks with a conchoidal or irregular fracture; Specific gravity: approx. 2.65.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, often with brownish or reddish tints from iron impurities; Luster: vitreous to dull; Crystal structure: hexagonal (as quartz); Cleavage: none, breaks with a conchoidal or irregular fracture; Specific gravity: approx. 2.65.
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. High heat and pressure cause the quartz grains to recrystallize and fuse together, typically in orogenic (mountain-building) belts.
Uses & applications
Used extensively in road construction, as railway ballast, and in the manufacturing of glass and ceramics. Polished varieties are used for countertops, flooring, and decorative stones.
Geological facts
Quartzite is so tough that it often outlasts the surrounding rocks during erosion, remaining as jagged ridges or hilltops. Unlike most rocks that break around their constituent grains, quartzite breaks right through the grains.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by a steel nail) and its grainy, sandpaper-like texture that doesn't rub off. It is commonly found in mountainous regions such as the Appalachian or Rocky Mountains.
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