corundum, geology.11, Madagascar.12, Ambondromifehy, Diego Garcia, gems

Since 1996, large quantities of yellow to blue sapphires have been recovered from alluvial deposits derived from basaltic rocks in northern Madagascar. The crystal morphology, internal growth patterns, mineral inclusions, absorption spectra, and trace element con-tents of these northern Madagascar sapphires are typical of “basaltic-magmatic” sapphires. Comparison of the properties of these sapphires to those of sapphires from different basaltic sources reveals no significant differences. The northern Madagascar sapphires are distinct from those from Andranondambo, a skarn-related deposit in southeastern Madagascar.