Spectroscopic Characteristics and Coloring Mechanisms of Different Colored Spinels from Myanmar

Abstract

Spinel is a common gemstone that has attracted the attention of gemologists worldwide because of its high refractive index, rich colors and brilliant hues. Myanmar is an important source of spinel. The present paper provides a systematic characterization of the gemological features of different color spinels from Myanmar, with a discussion and analysis of their color causes. The results show that complete octahedral crystal forms can be seen in Myanmar spinel, with the appearance of dissolution, growth motifs and cross-growth of crystals visible on the crystal surfaces. The XRF results show that the Myanmar red and orange spinel samples contain high levels of Cr, with the magenta sample having significant levels of Cr and the orange sample having more V. The blue and purple samples have high levels of Fe. The peaks of the infrared spectrum mainly appear around 841 cm−1, 690 cm−1 and 532 cm−1. Raman spectra have peaks mainly around 310 cm−1, 405 cm−1, 663 cm−1 and 764 cm−1. According to the UV-Vis spectrum, the color of Myanmar red and orange spinels is mainly due to Cr3+ and V3+. When the Cr3+ content is higher than the V3+ content, the spinels show a red hue; when the V3+ content is higher than Cr3+, the spinels have an orange hue. Blue color is due to the charge transfer between Fe2+ and Fe3+. The research in this paper has enriched the gemological characteristics of Myanmar spinel and can provide a theoretical basis for its investigation, marketability, design and utilization.