Inclusions, Chemical Composition, and Spectral Characteristics of Pinkish-Purple to Purple Spinels from Mogok, Myanmar

With the increasing market demand for spinels of various colors, purple spinel—long regarded as a symbol of nobility—has attracted growing attention. In this study, pinkish-purple to purple spinels from the Mogok region of Myanmar were systematically examined using conventional gemological, spectroscopic, and chemical analytical techniques. Raman analysis reveals that these spinels commonly contain octahedral inclusions composed of calcite, dolomite, magnesite, and graphite. Chemically, the samples are primarily magnesia-alumina spinels. Color variation is influenced by trace elements: increasing Cr and V contents enhance the red hue, while higher Fe concentrations intensify the purple tone. UV–Vis spectra show that Cr3+ and V3+ jointly contribute to absorptions at 388 nm and 548 nm, with Fe2+ and Fe3+ responsible for the bands at 371 nm and 457 nm, respectively, together controlling the pink-to-purple color variation. Most samples display four Cr3+-related peaks near 700 nm; however, these are absent in deeply purple spinels. In contrast, light pink spinels show weaker absorption at 371 nm and 457 nm, attributed to Fe2+ and Fe3+. Fluorescence spectra confirm characteristic Cr3+ emission bands at 673 nm, 684 nm, 696 nm, 706 nm, and 716 nm, indicating a strong crystal field environment. Raman spectra have peaks mainly around 312 cm−1, 406 cm−1, 665 cm−1, and 768 cm−1. The peaks of the infrared spectrum mainly appear around 840 cm−1, 729 cm−1, 587 cm−1, 545 cm−1, and 473 cm−1.