Rubies and sapphires from four deposits in Minas Gerais named Sapucaia, Indaiá and Palmeiras, in the region of Caratinga-Manhuaçu, and Malacacheta, farther north, were characterized in terms of geology, gemology, chemistry and spectroscopy in order to interpret causes of color and genesis. The economical potential of the deposits was also analyzed. Chemical analyses and UV-visible spectroscopy reveal that the probable cause of the blue color is a charge transfer between Fe2+ e Ti4+, while Cr3+ causes violet and purplish tints, alexandrite effect and fluorescence. Absence of Ce and La and relatively higher Ga-contents distinguish the Malacacheta samples from the others. Besides suggesting genetic particularities, the difference in terms of trace elements might be used as a provenience indicator for the gems. Inclusions of an Al2SiO5 polimorph and field evidences suggest that the origin of corundum might be due to regional metamorphic processes, thus expanding the possibilities for the discovery of new occurrences of ruby and sapphires in the high grade metamorphic terrain in eastern Minas Gerais.
Corundum; ruby; sapphire; Minas Gerais; trace-elements; gemology
