Contact resonance atomic force microscopy (CR-AFM) is a nondestructive technique based on atomic force microscopy (AFM) that allows one to perform single-point measurements as well as surface mapping of the indentation modulus of a material. In this work, we demonstrate the potential of CR-AFM in applied mineralogy research. As a case study, we report the characterization of natural and thermally treated diaspore. Natural diaspore samples from the Ilbirdagi diasporic metabauxite (diasporite) deposit in the Milas (Muğla) region in Turkey were heat treated in a muffle furnace causing them to transform from diaspore to corundum. After the treatment, the samples had a polycrystalline structure with ordered micrometer-size rectangular grains of uniform crystallographic orientation. Nanomechanical characterization by CR-AFM allowed us to visualize inclusions with different mechanical properties and to determine the average indentation modulus of the surface of the thermally treated diaspore. Quantitative maps of the indentation modulus reveal the variation of the indentation modulus on the surface of single micro-grains with nanometer spatial resolution.