Gemological, Colorimetric, and Spectroscopic Characteristics of Mali Garnets

Mali garnet is a gem-quality variety of the grossular–andradite solid-solution series and exhibits a wide range of colors, from near-colorless through light yellow, medium yellow, yellow, yellow-green, green with a yellow tint, to green. In this study, 38 faceted samples commercially represented as Mali garnet were investigated using energy-dispersive X-ray fluorescence (ED-XRF), ultraviolet–visible (UV–Vis) reflectance spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and Commission Internationale de l’Éclairage (CIE) 1976 L*a*b* (CIELab) colorimetry. The samples are dominated by SiO2, CaO, Al2O3, and Fe2O3. Fe2O3 ranges from 1.22 to 9.96 wt%, whereas Cr2O3 is generally low, mostly below 0.3 wt%. Fe3+ contents were stoichiometrically inferred from ED-XRF data, and trace-element data were treated as semi-quantitative. Inferred Fe3+ shows a positive trend with the CIELab yellowness parameter b*, whereas Cr-bearing samples tend to have more negative a* values and show a reflectance minimum near 582 nm. A Fe3+-related reflectance feature occurs at approximately 430–440 nm. FTIR spectra display an approximate red shift of the ν3 band from ~960 to ~940 cm−1, consistent with Fe3+ substitution for Al3+ at the Y site. In the a*–b* plane, the samples form a continuous distribution broadly corresponding to their visual colors. These observations are consistent with the color variation of Mali garnet being mainly associated with Fe3+ and Cr3+ contents: Fe3+ contributes to yellow hues, while Cr3+ enhances green hues. The observed trends provide a useful reference for understanding the color characteristics of Mali garnet and for further quantitative color–composition studies.