metamorphic
Quartzite
Quartzite (SiO2 composition)
Hardness: 7 on Mohs scale; Color: typically white to gray, but often pink or reddish due to iron oxides; Luster: vitreous to dull; Crystal structure: trigonal (hexagonal); Cleavage: none; 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 often pink or reddish due to iron oxides; Luster: vitreous to dull; Crystal structure: trigonal (hexagonal); Cleavage: none; Specific gravity: 2.6-2.7.
Formation & geological history
Formed through the regional metamorphism of quartzose sandstone. High heat and pressure cause the sand grains to recrystallize and fuse together into a dense, hard rock. Typically found in mountain belts where tectonic plates collide.
Uses & applications
Used in construction as crushed stone for road gravel and rail ballast, as dimension stone for building facades and flooring, and occasionally as a source of silica in glass manufacturing.
Geological facts
Quartzite is so hard and chemically resistant that it often forms the caprock or ridges of mountain ranges because it resists erosion much better than surrounding rocks like shale or limestone.
Field identification & locations
Identify it by its extreme hardness (cannot be scratched by steel) and its grainy, sugary texture. Unlike sandstone, when quartzite breaks, the fracture passes through the sand grains rather than around them.
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