metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, can be pink or red with impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (as quartz grains); Fracture: Conchoidal; Specific Gravity: 2.6-2.7.
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, can be pink or red with impurities
- Luster
- Vitreous to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white to gray, can be pink or red with impurities; Luster: Vitreous to dull; Crystal structure: Trigonal (as quartz grains); Fracture: Conchoidal; Specific Gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. Intense heat and pressure cause the quartz grains to recrystallize and fuse together, eliminating the original pore space and sedimentary texture.
Uses & applications
Used in construction as crushed stone for road gravel, railroad ballast, and building stone. Highly pure varieties are used in the production of glass, ceramics, and ferrosilicon.
Geological facts
Quartzite is so tough that it often survives intense weathering better than other rocks, frequently forming the peaks of mountain ranges. It is significantly harder than the sandstone it originates from.
Field identification & locations
Identify in the field by its extreme hardness (cannot be scratched by steel) and the way it breaks through the quartz grains rather than around them (unlike sandstone). Found globally in metamorphic belts such as the Appalachian Mountains and Scandinavian Caledonides.
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