Amorphous carbon is the name used for carbon that does not have any crystalline structure. As with all glassy materials, some short-range order can be observed, but there is no long-range pattern of atomic positions. General Name, Symbol, Number Carbon, C, 6 Chemical series Nonmetals Group, Period, Block 14 (IVA), 2, p Density, Hardness 2267 kg/m3 0. ... Quartz crystal A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... An amorphous solid is a solid in which there is no long-range order of the positions of the atoms. ...

While entirely amorphous carbon can be made, most of the material described as "amorphous" actually contains crystallites of graphite [1] (http://gltrs.grc.nasa.gov/reports/1996/CR-198469.pdf) or diamond [2] (http://www.iupac.org/goldbook/D01673.pdf) with varying amounts of amorphous carbon holding them together, making them technically polycrystalline or nanocrystalline materials. Commercial carbon also usually contains significant quantities of other elements, which may form crystalline impurities. Graphite (named by Abraham Gottlob Werner in 1789, from the Greek γραφειν: to draw/write, for its use in pencils) is one of the allotropes of carbon. ... A scattering of round-brilliant cut diamonds shows off the many reflecting facets. ...

In technical terms, true amorphous carbon has localized π electrons (as opposed to the aromatic π bonds in graphite), and its bonds form with lengths and distances that are inconsistent with any other allotrope of carbon. It also contains a high concentration of dangling bonds, which cause deviations in interatomic spacing (as measured using diffraction) of more than 5%, and noticeable variation in bond angle [3] (http://www.iupac.org/goldbook/A00294.pdf). In chemistry, an aromatic molecule is one in which electrons are free to cycle around circular arrangements of atoms, which are alternately singly and doubly bonded to one another. ... Allotropy (Gr. ... The allotropes of carbon are the different molecular configurations (allotropes) that pure carbon can take. ... Diffraction is the apparent bending and spreading of waves when they meet an obstruction. ...

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. Coal is a fossil fuel extracted from the ground either by underground mining, open-pit mining or strip mining. ... Soot, also called lampblack or carbon black, is a dark powdery deposit of unburned fuel residues, usually composed mainly of amorphous carbon, that accumulates in chimneys, automobile mufflers and other surfaces exposed to smoke—especially from the combustion of carbon-rich organic fuels in the lack of sufficient oxygen. ... Pyrolysis is formally defined as chemical decomposition of organic materials by heating in the absence of oxygen. ... Anthracite coal Anthracite is a hard, compact variety of mineral coal that has a high luster. ... Bituminous coal Bituminous coal is a soft coal containing a tar-like substance called bitumen. ... Coal Coal is a fossil fuel extracted from the ground by mining. ...

See also: Glassy carbon Diamond-like carbon Glassy carbon is a class of non-graphitizing carbon which is widely used as an electrode material in electrochemistry, as well as for high temperature crucibles and as a component of some prosthetic devices. ... Diamond-like carbon (DLC) is a term which covers many new forms of carbon which have both graphitic and diamond like characteristics. ...

Sources

1. Nasa TEM photos showing graphite crystals in soot (http://gltrs.grc.nasa.gov/reports/1996/CR-198469.pdf)
2. Discussion of hard "amorphous" carbon films (http://www.iupac.org/goldbook/D01673.pdf)
3. Definition, from International Union of Pure and Applied Chemistry (http://www.iupac.org/goldbook/A00294.pdf)