Described herein is a method and system for classifying rock types in a rock body. The method comprises the steps of obtaining spectral data from a spectral measurement (202) of a surface region of the rock body and then determining a first spectral ratio between two wavelength bands of the spectral data. From the first spectral ratio it can be assessed (204) whether the measurement is a high-angle measurement, and if the measurement is not a high-angle measurement then a further spectral ratio between two further wavelength bands of the spectral data is determined (208). The further spectral ratio is then compared (210) with a corresponding diagnostic criterion to assess whether the surface region comprises a first rock type associated with the further spectral ratio and diagnostic criterion.