The influence of Vietnam and Sri Lanka spinel mineral chemical elements on colour

The chemical composition of 42 various colour spinel minerals from the Vietnam Luc Yan locality and the Sri Lanka Ratnapura locality were investigated and according to the results of the research the chromophore influence on colour was interpreted. It was established that the colour of spinel mineral is determined not only by chromium, iron, cobalt but also by vanadium. We assume that V3+ determines the brown or yellow spinel colour, since a relatively high content of V2O3 (0.44-0.88%), which may determine the orangey hue of mineral, was found in the investigated orangey pink samples from the Ratnapura locality. Other chromophores found in these samples, such as chrome oxide (0.05-0.36%), iron oxide (0.08-0.28%) and cobalt oxide (0.05-0.20%), show low or medium contents, which determined the pink hue of spinel. After carrying out the research on the samples of dark red spinel, it was established that the red colour is determined by a high content of Cr3+. The purple/violet colour of samples is determined by Fe2+ and a low content of Co2+, whereas the pink hue of samples is determined by Cr3+ and a high content of Fe2+, which saturation depends on the quantitative ratio of Fe2+ and Cr3+. Relatively low contents of chromophores V3+, Cr3+, Fe2+ and Co2+ were found in the pinkish grey spinel, thus their hue is grey.