Various chemical elements are critical for our clean energy transition (e.g., producing lithium-ion batteries for electric vehicles). Many of these critical elements are associated with a type of magmatic deposit: lithium-cesium-tantalum (LCT) pegmatites. These LCT pegmatites have been studied in detail, but different schools of thought still exist on the formation conditions. Especially the role of the high concentration of fluxing components and the associated formation of critical elements-bearing minerals remains a puzzling phenomenon. A detailed three-dimensional (3D) characterization of mineralized LCT pegmatites is paramount in improving our knowledge of their formation history. This project investigates the commonly observed complexity of the various mineral assemblages within extended core samples of LCT pegmatites. I developed a methodology that combines two-dimensional microbeam imaging techniques with X-ray computed tomography to image the mineralogical and textural variability of geological samples in 3D. This will enable me to study for the first time the role of fluxing components in the subsequent formation stages and to pinpoint the crucial stages that will allow critical element mineralization during LCT pegmatite formation. This is crucial to verify proposed formation models and experimental simulations. Ultimately, this will contribute to fundamentally new concepts on the formation conditions of mineralized LCT pegmatites.