Analysis on Chemical Composition and Heat Treatment Result of Light Yellow Scapolite

The scapolites are relatively common minerals in nature. Those ones with rich colour, high transparency and larger sizes are used in gems. In this paper, 12 pieces of light yellow scapolite samples from Africa were tested by conventional gemmological methods, and 3 pieces of scapolite samples were selected randomly for laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for chemical composition. Utilizing anion analysis, the LA-ICP-MS data showed that this batch of samples were dipyres in the scapolite group. Moreover, in order to determine the effect of heating temperature, holding time and atmosphere on its colour and to obtain the most effective treatment parameters, different heating processes were designed. During the heating process, the authors added activated carbon powder to create a reducing atmosphere. UV-Vis spectra were obtained and compared before and after heat treatment. The formula of fading colour was used to analyze the efficiency of colour change so that the best conditions for heat treatment of scapolites can be determined. Consequently, to summarize, heating to 600℃ and keeping for 6 hours, the colour of scapolite samples could fade dramatically from light yellow to colourlessness, and the reduce rate of colour purity was 64.57%.