The spectroscopic characteristics of ruby from various deposits: Myanmar, Mozambique and Thailand

Ruby derives its familiar red color from replacement of Al3+ ions in the corundum (Al2O3) matrix by Cr3+ ions. As trace elements also have effects on the color, it exhibits a delicate difference according to the deposits. Rubies are produced in three types of primary deposits such as marble-hosted, basalt-hosted, and metasomatic. We investigated different deposits using UV-Vis, FTIR and WD-XRF spectroscopy. Myanmar has the world's finest rubies, containing the lowest in Fe formed in the regional metamorphism of limestone by heat and pressure as marble-hosted deposits. However, Mozambique rubies contain a lot of trace elements with the lowest in Si, and appear to be formed at the metasomatic deposits as desilicated pegmatites intruding silica-poor rocks. Metasomatism is a metamorphic process that chemical components exchange with the existence of fluids. Basalt-hosted deposits are related to the process whereby the alkali basalt magma brings corundum to the surface. Containing lots of Fe and Si, Thailand rubies are considered to originate from basalt-hosted deposits. UV-Vis spectroscopy showed that Myanmar rubies differed from Mozambique and Thailand rubies. Mozambique and Thailand rubies showed absorption in the vicinity of 410 and 560 nm, while some Myanmar rubies had absorption at around 440 and 518 nm. Furthermore, small transmissions were observed between the two absorption bands. These findings confirm why Myanmar ruby results in a strong red color. Myanmar rubies have clouds of fine dust of rutile and liquid droplets of reticulated "feathers". Mozambique rubies showed lamella twin planes and lines. The most distinctive feature was curved rutile. Thailand rubies were mainly observed to be crystal, and negative crystal.