Mineral dust exerts wide-ranging influences on climate, atmospheric chemistry, and ecosystems, yet its compositional heterogeneity remains poorly represented in global impact assessments. Here, we provide observational constraints and process-level understanding of the compositional variability of long-range transported Saharan dust, including inorganic ions, crustal elements, and trace metals, sampled at the High Altitude Research Station Jungfraujoch (3580 m above sea level) during major dust intrusions between 2011 and 2021. Crustal elements dominate <em>PM</em>₁₀ (~45 % from Si, Al, Fe, Ca, K, and Mg) and exhibit the strongest enrichment relative to background concentrations (e.g. factor ~60 for Ti). However, compositional variability differs markedly among species, spanning nearly an order of magnitude for Ca, CO₃^2-, S, and Pb, but remaining below a factor of two for Fe and Ti. Combining aerosol observations with satellite remote-sensing retrievals and atmospheric reanalysis, we identify dust source regions and transport history as first-order controls on Saharan dust composition far from source. Soil mineralogy leaves persistent signatures that remain detectable after transcontinental transport, including variations in sedimentary carbonate and clay minerals governing Ca, CO₃^2-, and alkali metal fractions. Superimposed, atmospheric processing modifies dust composition through interactions with anthropogenic pollution and size-selective transport, leading to sulfate and heavy-metal accumulation, enhanced crustal-element solubility, and depletion of coarse-mode species like rare earth elements through gravitational settling. These findings demonstrate that mineral dust is not a passive tracer but a compositionally evolving vector linking desert emissions with climate, atmospheric chemistry, and biogeochemical cycling on a global scale.