metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but often yellow or reddish due to impurities; Luster: vitreous to waxy; Crystal structure: hexagonal (as constituent grains); Breakage: conchoidal or irregular fracture across grains.
- Hardness
- 7 on Mohs scale
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 on Mohs scale; Color: typically white, gray, or tan, but often yellow or reddish due to impurities; Luster: vitreous to waxy; Crystal structure: hexagonal (as constituent grains); Breakage: conchoidal or irregular fracture across grains.
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. Intense heat and pressure cause the individual sand grains to recrystallize and fuse together. It can originate from sedimentary rocks dating back billions of years or as recently as several hundred million years.
Uses & applications
Used in construction as road ballast, gravel, and building stone. Highly polished semi-translucent specimens are used in lapidary for beads and ornamental carvings. Also used as a raw source of silica for glass manufacturing.
Geological facts
Quartzite is one of the most durable and weather-resistant rocks on Earth. Unlike sandstone, which breaks around its grains, quartzite breaks directly through the quartz grains because the rock is so well-cemented.
Field identification & locations
Can be identified in the field by its grainy, sugary texture and extreme hardness (will scratch glass). Commonly found in folded mountain belts and as river-worn cobbles in glaciated or high-energy stream environments. Collectors should look for unique colors or translucency.
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