Calcite is the most important mineral in Asian dust, and it reacts with atmospheric gases during its long-range transport. Mineralogical and chemical analyses of Asian dust and source soils showed two types of calcite that differ greatly in morphology and origin: (i) micron-sized irregular particles derived from the erosion of bedrock, and (ii) nanosized fibers that were chemically precipitated in soils. In Asian dust aerosol particles, these nanofibers were internally mixed with clay minerals, often coating quartz and feldspar grains together with clay minerals. Nanofiber-bearing aerosol particles were more abundant than the coarser calcite particles. The nanofibers reacted to form sulfate coatings on minerals, providing a significant contribution to the optical, chemical, and hygroscopic modifications of Asian dust due to their enhanced reactivity. Asian dust is basically a mineral aerosol, and its mineralogical diversity needs to be characterized before a proper estimation of its climatic, geochemical, and ecological roles and provenance.