It is essential to expose the rock’s heterogeneous microstructure and micro-mechanical properties for understanding the macroscopic deformation and failure. In this paper

atomic force microscopy (AFM)

combined with powder X-ray diffraction (XRD)

scanning electron microscopy (SEM) and energy dispersive spectrum (EDS) techniques

is used to analyze the nanoscale mineral composition and microstructure of slate taken from Sichuan-Tibet railway tunnels. The spatial distribution of Young’s modulus is revealed at the microscale. The average Young’s modulus and probability of high

medium and low strength phases are determined by statistical deconvolution of more than 1.6 million test data using a mixed Gaussian model. The upscaling of Young’s modulus of slate is carried out based on the Mori-Tanaka model. A cross-scale characterization method of Young’s modulus is proposed based on the Mori-Tanaka model and micro-mechanical properties of minerals. The results show that: (1) The quartz embedded in the slate is a convex polygon block

the thin illite sheets are closely arranged with obvious stratification

and the chlorite is loosely distributed in the micro-pores as the matrix; (2) The adhesion of quartz

illite

chlorite and micro-pore to the probe increases in turn

and the Young’s modulus decreases; (3) The porosity of slate is 16.61%

and the equivalent Young’s modulus at the macroscale is 56.17 GPa. This approach can be used to determine the mechanical properties of fractured

small-size and arbitrary-shaped hard rock

which can overcome the difficulty of collecting large-size samples of engineering rock.