Shale shear fracture mirrors are key indicators of localized shear deformation, yet their high reflectivity origin remains unclear. This study employs electron microscopy and Raman spectroscopy to analyze fracture mirrors from the Lower Cambrian Qiongzhusi shale. Results reveal the shiny surface is not merely a product of mechanical polishing but is primarily attributed to the formation of highly ordered nanocoatings on fracture surface. The coatings comprise aligned clay minerals and, crucially, organic materials that have undergone shear-induced partial graphitization. Transmission electron microscopy reveals a about 0.46 nm lattice fringe spacing, and Raman spectroscopy confirms a moderate structural order and an elevated thermal maturity of organic matter. This transformation yields a dense material dominated by ultra-micropores, which minimizes light scattering of fracture surface. The formation of fracture mirrors results from shear displacement and frictional heating, which lead to mechanical comminution and microstructural reorganization. This finding establishes the shear fracture mirrors as the key indicators for revealing beddingparallel slip history in shale-involved detachment and, more practically, for assessing fluid migration pathways, seal integrity, and natural fracture networks in shale gas systems.

Atomic force microscopy coupled with infrared spectroscopy (AFM-IR) is one of the most effective and widely employed mixed techniques capable of providing direct access to infrared spectroscopic imaging and chemical analysis at the nanoscale spatial resolution. In this communication, AFM-IR was applied to the evaluate the in-situ nanoscale mineralogy and to characterize the organic structure of shale. Significant chemical and microstructural heterogeneity could be observed on the mirror-like surface of naturally deformed shale. It was also apparent that slickensides formed on the mirror-like surface potentially influence the spatial distribution of organic matter. This technique provides an effective combination for direct and in-situ studies of the morphology and physicochemical properties of geological rocks at the nanoscale, opening a new avenue for investigations to help reveal some complex geological phenomena, such as organic carbon graphitization and mineral transformation during fault deformation. Furthermore, this technique makes it possible to determine the chemical composition, molecular structure and functional group information of shale organic matter, which is crucial information for investigating the hydrocarbon generation potential, maturity evaluation, and oil and gas migration mechanisms in shale.