Described herein is a method and system for characterizing in-ground rock types from measurement-while-drilling data in a mining environment. The method includes the steps of drilling holes at a plurality of selected locations within a region of interest; collecting measurements while drilling to obtain an array of data samples (162) indicative of rock hardness at various drilling depths in the drill hole locations; obtaining a characteristic measure (163) of the array of data samples; performing Gaussian Process regression (164) on the characteristic measure; and applying boundary detection (166) to the rock hardness output data obtained from the Gaussian process model to identify the distribution (280) of at least one cluster of rock type within the region of interest.