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This study compares two purple gem spinel samples with regard to trace element chemistry and visible light absorption spectra, and presents the first reported example of a spinel with a saturated purple color caused predominantly by chromium and cobalt. Sample VN, from a placer deposit in the Luc Yen district of Vietnam, exhibited strong saturation, orange-red fluorescence in UV, and magnesite and graphite inclusions. Sample AF was from Badakhshan, Afghanistan, with light to medium saturation and containing phlogopite, amphibole, and probable fluid inclusions. UV-Vis-NIR spectra are compared along with trace element chemistry. Sample VN is colored primarily by cobalt (17.9 ppma) and chromium (593 ppma), with minor color contribution from Fe (2437 ppma), and contains significantly more cobalt than typical Cr-enriched red, pink, and purple gem spinels (<6 ppma Co). The dominant contributions of chromophores Cr3+ and Co2+ to the color of sample VN are responsible for its higher color saturation than that of sample AF, which is colored dominantly by Fe2+ and Fe3+ (3089 ppma total Fe) and contains negligible concentrations of other chromophores (<10 ppma V3+, Cr3+, and Co2+). In the Vietnamese purple spinel, the relatively low Fe concentration is likely crucial in creating the attractive saturated color. This sample is enriched in Co, Ni, Cr, V, Zn, and Ga. In contrast, the purple spinel from Afghanistan is relatively impoverished in all trace elements except Fe and Mn. Sample VN represents an approximate intermediate between natural gem spinel populations colored dominantly by Cr3+ vs. dominantly by Co2+. Cr3+-, (Fe2+, Fe3+)-, and Co2+-dominant (in terms of color) gem spinels are easily differentiated by chemical composition using a discrimination plot of Co/Cr vs. Co/Fe, but this is not valid for spinel dominantly colored by V3+ or containing significant concentrations of Fe. [ABSTRACT FROM AUTHOR]

The article focuses on orthorhombic aluminum oxide hydroxide mineral with the formula AlO is a relative newcomer to the jewelry scene with some stones possessing a captivating ability to change color between pale green, yellow, pink, and purple when viewed in different sources of light. Topics include the document a new find of purplish pink gem diaspore reportedly from Nangarhar Province, Afghanistan, and the transparent crystals of diaspore in sizes suitable for jewelry purposes.