Geographical division We will distinguish: 1 the volcanic solid mass of Androy, it is covered with thorny bush and meadows.
2 the gneissic zone of to Mandrarean Androy, fields plains and hills, rare zones of savanna on of red ground At the time calcareous carapace. of the great Altitude varies there from dryness in 600 meters on the hills the south. to 250 meters at the bottom.
3 the western slope of the high Anosyans chains which tops are staged between 1500 and 2000 meters. It is a field of meadows.
Geological divisions. 1 Crystalline schists. Gneiss with diopside, syenitic eysies gneisses, arteritic injections, gneiss at cordierite, etc. 2 Old eruptive rocks. Pegmatites, Dissogénites, Esirians granites , charnockites, kalambatreans granites, late granites . 3 Recent eruptive rocks. (Volcanic solid mass of Androy) a) A the base, a thick basaltic subhorizontale series . b) Basaltic dykes. On the road to Andranondambo c) A thick higher subhorizontale rhyolitic series. d) Rhyolitic dykes . 4 Recent formations. If russet-red sands are excluded, the recent formations have only a very weak development. It is necessary to quote the alluvial plains of Androtsy, Esira, Sangoria and Pisopiso. A notable calcareous carapace covers most of the area.
Metamorphized dolomitic limestone. Near Andranondambo
The anosyans granites are regarded as synorogenes, eocambrians formed in the androyans series to which an age higher than 2400 MY is allotted.
The esirians granites present very variable crushings of intensity which often give them a gneissic facies . There is sometimes passage to orthogneisses. General foliation is sub meridian.
The occurrences of the Andranondambo area were industrially exploited since 1993 and have been almost abandoned few years later. Actually, it is very difficult to exploit sapphire direct in mother rock, because corundum is not concentrated enough. Furthermore, the hardness of the rock makes its exploitation very expensive.
