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Amorphous carbon is free, reactive carbon that does not have any crystalline structure. Amorphous carbon materials may be stabilized by terminating dangling-π bonds with hydrogen. As with other amorphous solids, some short-range order can be observed. Amorphous carbon is often abbreviated to aC for general amorphous carbon, aC:H or HAC for hydrogenated amorphous carbon, or to ta-C for tetrahedral amorphous carbon (also called diamond-like carbon).[1]
In mineralogy, amorphous carbon is the name used for coal, soot, carbide-derived carbon, and other impure forms of carbon that are neither graphite nor diamond. In a crystallographic sense, however, the materials are not truly amorphous but rather polycrystalline materials of graphite or diamond[2] within an amorphous carbon matrix. Commercial carbon also usually contains significant quantities of other elements, which may also form crystalline impurities.