metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, often with pink or reddish tints from iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, breaks with a conchoidal or irregular fracture; Specific gravity: 2.6-2.7
- 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 pink or reddish tints from iron oxides; Luster: vitreous to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none, breaks with a conchoidal or irregular fracture; Specific gravity: 2.6-2.7
Formation & geological history
Formed through the regional or contact metamorphism of quartz-rich sandstone. Under intense heat and pressure, the individual quartz grains recrystallize and fuse together. Often found in Precambrian mountain belts or fold mountain ranges.
Uses & applications
Used as a decorative stone in architecture, as crushed stone for road construction and railway ballast, and in the manufacturing of glass and ceramics due to high silica content.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than along their boundaries, unlike the sandstone it originated from. Some varieties include 'fuchsitic quartzite' which can be bright green.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel nail) and grainy, sugary texture. It is commonly found in mountainous regions such as the Appalachians or the Alps. Collectors look for unique colors or banding.
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