Inclusion and Spectral Characteristics of Sapphire from Ilakaka, Madagascar

The inclusions and spectral characteristics of blue and orange sapphire from Ilakaka, Madagascar have been studied by Raman spectroscopy, infrared spectroscopy, LA-ICP-MS, UV-Vis-NIR absorption spectroscopy and fluorescence spectroscopy. This study aimed to enrich the information of characteristics of sapphire from Ilakaka, Madagascar.The results showed that the characteristic inclusions of sapphire from Ilakaka included a large number of liquid CO₂-filled negative crystals and healed fissures filled with pseudosecondary inclusions such as goethite and sulfur. It also contained a variety of solid inclusions, such as calcite, graphite, phlogopite, rutile, hematite and kaolinite. The content of Fe in sapphire was positively correlated with the intensity of blue tone.The absorption lines at 377, 387 nm and 451 nm associated with Fe³⁺ were found in all types of sapphire, and the increase of Fe content could promote the formation of Fe³⁺-Fe³⁺ exchange-coupled ion pairs and enhance the absorption at 377 nm and 451 nm. R₁ (694 nm) and R₂ (693 nm) fluorescence lines of Cr³⁺ were observed in the fluorescence spectra of almost all samples. Orange sapphires had wide fluorescence peaks at 400-480 nm. The low temperature annealing experiment showed that these fluorescence peaks had poor thermal stability and tended to disappear when heated to 250 ℃, while the fluorescence peaks increased significantly when heated to 300 ℃. The thermo behavior of those florescence peaks may be associated with hole centers [V_Al+O^-] and [Mg²⁺+O^-].