All varieties of solids consisting mainly of the element carbon with two-dimensional long-range order of the carbon atoms in planar hexagonal networks, but without any measurable crystallographic order in the third direction (c
-direction) apart from more or less parallel stacking.
Some varieties of non-@G02689@ convert on heat treatment to @G02689@ but some others do not (@N04194@).
See also: amorphous carbon
PAC, 1995, 67, 473. 'Recommended terminology for the description of carbon as a solid (IUPAC Recommendations 1995)' on page 498 (https://doi.org/10.1351/pac199567030473)