2.2.1. Deposits in feldspathic gneisses
The Sahambano deposit, 30 km east of Ihosy town (Fig. 1), was
discovered in 1999 and is exploited by themining company TanyHafa S.A.
The sapphire crystals are multicoloured but rarely of gem-quality, and
treatment is necessary to improve colour and transparency: 100 kg of
corundum picked in the washed material contained 24 kg of coloured
sapphires with 1 kg of translucent crystals, but only 50 g of gem-quality
(Offant, 2005). The division of the colour is 15% brown to orange, 5%