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Description
Quartzite is generally buff to pale brown, but it can be almost any color, depending on the chemical impurities present. Samples often display a sugary appearance on a freshly broken surface. Metamorphosed quartzite can be distinguished from silica-cemented sandstone by careful inspection of a fresh surface: In sandstone, the rock breaks around mineral grains, while in quartzite, the rock breaks through the grains.
Physical Properties
Quartzite's properties are similar to those of the mineral quartz. A sample of quartzite has a density of approximately 2.3 to 2.4 g/cc. The rock type's hardness of approximately 7 on the Mohs hardness scale makes it very resistant to weathering. Porosity is generally low to very low.
Terminology
The word "quartzite" has been applied to both the quartz-rich metamorphic rock and to unmetamorphosed hard, silica-cemented sandstone comprising nearly pure quartz grains. Use of the term for a sedimentary rock is discouraged in favor of "orthoquartzite" to reduce confusion.