The accelerating global demand for critical minerals such as lithium, rare earth elements (REE), and nickel is transforming the mining industry and placing increasing pressure on operations to improve efficiency, reduce energy consumption, and ensure long-term sustainability. In this context, advanced mineralogical tools are essential for reducing geological, metallurgical, and economic risk across the entire mining value chain. X-ray diffraction (XRD), when integrated with advanced statistical and multivariate methods such as Rietveld refinement, cluster analysis, and Partial Least Squares Regression (PLSR), provides a robust and predictive framework for mineralogical domain definition, geometallurgical modelling, process optimisation, and sustainable energy management. This paper presents four integrated case studies demonstrating the strategic value of XRD in critical minerals mining: (i) nickel laterite deposits, (ii) hard rock lithium ores, (iii) REE exploration samples, and (iv) prediction of mill energy consumption through Bond Work Index (BWi) modelling. In nickel laterites, XRD enables detailed characterisation of mineralogical zonation within saprolite and laterite horizons, supporting grade control, ore blending, and optimised processing routes. In lithium systems, XRD provides accurate quantification of lithium-bearing phases and supports prediction of processing performance and mineral transformation efficiency. In REE exploration, XRD combined with clustering techniques allows mineralogical domain classification, improving geological modelling and exploration targeting. Beyond resource characterisation, XRD-derived mineralogical data are directly linked to energy-intensive processes such as comminution, where mineralogy controls grindability and energy demand. By integrating XRD with PLSR and BWi modelling, predictive energy models can be developed to support Mine to Mill optimisation and energy-efficient circuit design. Collectively, these case studies demonstrate that XRD-based mineralogical analysis is not merely descriptive, but forms a strategic foundation for geometallurgy, mine planning, process optimisation, and sustainable energy management in critical minerals mining and processing.