In Mineralogy
Historically, the term "amorphous carbon" was used to describe carbonaceous materials found in soot and coal that could not be categorized as either diamond or graphite. However, these materials are not truly amorphous, but consist of crystallites of graphite or diamond technically polycrystalline or nanocrystalline materials. Commercial carbon also usually contains significant quantities of other elements, which may form crystalline impurities.
Coal and soot are both informally called amorphous carbon. However, both are products of pyrolysis, which does not produce true amorphous carbon under normal conditions. The coal industry divides coal up into various grades depending on the amount of carbon present in the sample compared to the amount of impurities. The highest grade, anthracite, is about 90 percent carbon and 10% other elements. Bituminous coal is about 75-90 percent carbon, and lignite is the name for coal that is around 55 percent carbon.
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