Spectral Characteristic and Chemical Composition of Ruby from Southwest Kenya

Rubies from Kenya in Africa currently occupy a significant portion of the color-stone market, there are still needs for additional spectral characteristic and chemical composition information. In this study, the gemmological characteristics and chemical compositions of 40 pieces of ruby samples from southwest Kenya were investigated by conventional gemmological test instruments, FTIR spectrometer, Raman spectrometer, laser ablation inductively coupled plasma mass spectrometer(LA-ICP-MS), ultraviolet-visible spectrometer(UV-Vis), and other test instruments, to explore the spectral characteristics and chemiacal compositions of the ruby samples from southwest Kenya, and to provide data for the origin identification of ruby. The results show that the refractive index of the ruby sample is 1.759 to 1.778, the birefringence is 0.009 to 0.010, and the relative density is 3.95 to 4.01. The ruby samples show weak to medium red fluorescence under long-wave ultraviolet fluorescence and none to weak fluorescence under short-wave ultraviolet fluorescence. The ruby samples contain inclusions included diaspore, rutile, chromite, amphibole, apatite and mica. These inclusions show no sign of heat treatment. The content of Al₂O₃ of the ruby samples range from 95.8% to 97.1%, the trace elements show high Cr, medium Fe and low V featurs. There is a positive correlation between the saturation of red and the contents of Cr. The contents of Fe, Cr, V, Ga could distinguish ruby samples from southwest Kenya with rubies from other origins. The hue of the ruby samples are red to purplish red, the saturation mainly ranges from vivid red to intense red. The proportion of vivid red ("Pigeon's blood" red) are about 40% of ruby samples from Kenya.