Mineralogical and Compositional Characteristics of Argentine Red–White Banded Rhodochrosite with Ca-Poor White Bands

Three commercial red–white banded rhodochrosite samples sold as Argentine “Rosa del Inca” material were investigated using conventional gemological observation, mineralogical analysis, micro-area chemical analysis, and spectroscopy. The red and white bands differ in color, transparency, and microstructure. However, both bands are mainly rhodochrosite. No evidence indicates that calcite, dolomite, or other Ca-bearing carbonate minerals are the main phases in the white bands. Representative EPMA analyses of LMK-02 show that the analyzed white-band points tend to contain slightly lower Mn and relatively higher Fe and Mg than the red-band points, while CaO is below the detection limit at all representative EPMA positions. Micro-XRF mapping of LMK-02 reveals only local and discontinuous enrichments of Ca and Zn; however, the mineralogical identity and occurrence mode of these enriched domains remain unresolved. Combined with the EPMA data, the XRD, FTIR, Raman, and UV–Vis results do not support marked Ca enrichment, extensive Ca substitution for Mn, or abundant Ca-bearing carbonate phases in the analyzed white bands of LMK-02. Instead, the results indicate Ca-poor compositional variation within rhodochrosite, with the representative EPMA data showing a descriptive tendency toward slightly lower MnO and relatively higher FeO and MgO contents in the analyzed white-band points.