Anthracite and coal-based graphite (CBG) samples were collected at varying distances from a granite intrusion. Optical microscopy, X-ray diffraction, Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) were used to characterize the structural evolution of CBG at different scales. The results indicated differences in the graphitization rates of coal macerals and crystallization degree of different graphite-like particles. Differentiated graphitization of coal was caused by deformation, which led to the discontinuous distribution of CBG. This indicates that samples located at the same distance from the intrusion were graphitized to different degrees or that CBG with a similar graphitization degree occurred at varying distances from the intrusion. A possible mechanism for graphitization is strain-induced graphitization, where the local stress concentration leads to preferred orientations of the basic structure units (BSUs), as well as the motion and rearrangement of structural defects, resulting in the formation of a locally ordered structure. The graphitization degree is enhanced as the local graphite structure spreads.

The graphitization of coal is complicated due to multiple factors, such as magmatic intrusions, tectonic stresses and the catalysis of minerals. Heterogeneous graphitization was found based on the nanostructural characterization of anthracite and coal-based graphite. It was determined that the graphitization of coal is not only the rearrangement of carbon layers but also the extinction of structural defects, as revealed by the evolution of XRD and Raman spectra and structural parameters (i.e., the interlayer spacing d002 and R2). Based on a comprehensive analysis of the nonstructural evolution of coal, the graphitization of coal could be divided into four stages at the nanoscale. The first stage (d002 > 0.344 nm and R2 < 0.7) is the transition process from coalification to graphitization, the second (0.337 nm < d002 ≤ 0.344 nm and R2 > 0.65) is the crystallization of carbon layers, the third stage (0.337 nm < d002 ≤ 0.344 nm and R2 ≤ 0.65) is characterized by the elimination of structural defects and straightness of carbon layers, and the fourth stage (d002 ≤ 0.337 nm and R2 ≤ 0.6) shows that the locally ordered graphite structure expanded to the whole sample.