metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be pink or reddish due to hematite inclusions; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (parent quartz grains); Fracture: Conchoidal to irregular; 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, but can be pink or reddish due to hematite inclusions; Luster: Vitreous to dull; Crystal structure: Trigonal/Hexagonal (parent quartz grains); Fracture: Conchoidal to irregular; Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the regional metamorphism of quartz-rich sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together, losing original sedimentary structures. Often found in Precambrian or Paleozoic geological formations.
Uses & applications
Used in construction as crushed stone for roadbeds and railroad ballast, as dimension stone for counter tops and flooring, and occasionally in glassmaking if pure enough. Small polished pieces are popular for landscaping and aquarium decor.
Geological facts
Quartzite is so hard that it can scratch glass and steel. Unlike sandstone, when broken, quartzite breaks through the quartz grains rather than around them. It is one of the most durable materials on Earth.
Field identification & locations
Identify in the field by its hardness and granular texture. Look for its tendency to break through quartz grains. Commonly found in folded mountain ranges like the Appalachians or the Alps. Collectors look for unique banding or coloring caused by mineral impurities.
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