gems, corundum, Madagascar.12

Sapphires from northern Madagascar. In the past few years, several new and important sapphire deposits have been discovered in Madagascar. Dr. Margherita Superchi, of CISGEM, Milan, Italy, described a new occurrence at Ambondromifehy, in Antsiranana Province, in the northern part of the island. The sapphires found to date were alluvial, having been weathered from basaltic rocks that were emplaced intermittently during the period from the Upper Oligocene to the Pleistocene. The sapphires are thought to be xenocryts; that is, they did not crystallize from the basaltic magma, but simply were transported by it. They are associated with zircon, spinel, pyroxene, and olivine. Dr. Superchi and her colleagues (A. Donini, D. Muzzioli, and E. Roman) obtained detailed gemological data, chemical compositions, and optical and Raman spectra for 74 crystals (the largest being 182.59 ct) and 13 cut stones. Among the more interesting discoveries were inclusions of pyrochlore, zircon, and sodic plagioclase, which, with the chemical data (e.g., high gallium contents) confirm the “basaltic” association of these sapphires (see the earlier abstract on gem corundum).