metamorphic
Quartzite
Quartzite (primarily SiO2)
Hardness: 7 on Mohs scale; Color: typically white to gray, but can be pink or reddish; Luster: vitreous to dull; Crystal structure: non-foliated, interlocking granoblastic quartz grains; Cleavage: none (conchoidal fracture).
- Hardness
- 7 on Mohs scale
- Color
- typically white to gray, but can be pink or reddish
- 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; Luster: vitreous to dull; Crystal structure: non-foliated, interlocking granoblastic quartz grains; Cleavage: none (conchoidal fracture).
Formation & geological history
Formed through the regional metamorphism of quartz sandstone. High heat and pressure cause the original quartz grains to recrystallize and fuse together, creating a dense, hard rock. Most significant deposits range from Precambrian to Paleozoic ages.
Uses & applications
Used in construction as crushed stone for road ballast, floor tiles, and countertop surfaces. High-purity quartzite is used to produce ferrosilicon, industrial silica sand, and silicon metal for electronics.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caprock or ridges in mountain ranges because it weathers much more slowly than surrounding rocks. Unlike sandstone, when quartzite is broken, it fractures through the quartz grains rather than around them.
Field identification & locations
Identify in the field by its inability to be scratched by a steel knife and its sugary, crystalline texture. It is commonly found in mountain belts such as the Appalachians, the Waterton-Glacier International Peace Park, and various shield areas worldwide.
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