A diffractometric method is proposed which characterizes coal as a ＇heterogeneous system＇. The method represents an alternative to microscope-based petrographic analyses. A high-volatile bituminous coal was chemically and petrographically characterized. It was then demineralized and separated into its main organic fractions on the basis of density. The coal as a whole and its organic constituents were examined by X-ray diffraction analyses, to which the radial distribution function was subsequently applied. The method (1) is an alternative to the microscopic method, (2) is fast and reliable, and (3) can provide an important contribution to the determination of the vitrinite content, a key variable in coal reactivity.