A
pitch with a complex mixture of numerous essentially aromatic
hydrocarbons. It does not contain anisotropic particles detectable by optical microscopy. Mesogenic
pitch is low in quinoline-insoluble fractions and capable of transforming into
mesophase pitch during continuous heat treatment above

by the formation of optically detectable
carbonaceous mesophase.
Source:
PAC, 1995, 67, 473
(Recommended terminology for the description of carbon as a solid (IUPAC Recommendations
1995))
on page 496