Amorphous carbon

Amorphous carbon is free, reactive carbon that does not have any crystalline structure (also called diamond-like carbon). Amorphous carbon materials may be stabilized by terminating dangling-π bonds with hydrogen. These materials are then called hydrogenated amorphous carbon. As with all 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.

In mineralogy

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, these materials are not truly amorphous, but are polycrystalline materials of graphite or diamond within an amorphous carbon matrix. Commercial carbon also usually contains significant quantities of other elements, which may also form crystalline impurities.