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- Title
Cobalt-Blue Spinel from Northern Pakistan.
- Authors
Schollenbruch, Klaus; Blauwet, Dudley; Malsy, Anna-Kathrin; Bosshard, Vera
- Abstract
Blue spinel coloured by cobalt was recently found near the Hunza Valley of northern Pakistan. Characterisation of 35 samples showed that hue variations ranging from bright blue to violet-blue to dark blue are due to variable relative concentrations of the colour-causing elements Co, Fe and Cr. Most of the spinels were semi-transparent and contained abundant internal features, including fractures, twin lamellae and growth structures, as well as distinctive iridescent geometric sectors. Solid inclusions consisted of rutile, zircon, apatite, phlogopite and calcite; fluid inclusions were rare. Samples displaying bright blue colouration typical of so-called Co-spinel had strong absorptions due to Co2+ along with subordinate Fe2+ features in their UV-Vis spectra, and contained relatively low ratios of Fe/Co (<110) and Cr/Co (<4).
- Publication
Journal of Gemmology, 2021, Vol 37, Issue 7, p726
- ISSN
1355-4565
- Publication type
Academic Journal
- DOI
10.15506/JoG.2021.37.7.726