Nano inclusions in sapphire samples from Sri Lanka

The turbid/translucent, near colorless (milky) metamorphic sapphire samples from Sri Lanka have been characterized after the heat treatment in N-2 at 1650 degrees C. As-received sapphire specimens became bluish-colored and exhibited more clarity after the heat treatment. It was found that the color change at inclusions zoning region is attributed by the dissolution. As received samples contain the micro/nano inclusions such as rutile (TiO2), ilmenite (FeTiO3), spinel (MgAl2O4)/ulvospinel (Fe2TiO4) and apatite (Ca-5(PO4)(3)), which were dissolved by the heat treatment and form the blue color through Fe2+/Ti4+ charge transferring. The microstructures become different because as the dissolution of apatite (Ca-5(PO4)(3)(OH,F,Cl)) in alumino silicates (Al2SiO5) occurred, resulting in morphological change with the appearance of (Ca, Mg, Al) silicate on the surface. Both as -received and heat treated samples showed the rhombohedral crystal structure of Al2O3.