Ilakaka Madagascar ( Sapphire rush )Written by Alain Darbellay GGGems
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· VOHIMENA VAOVAO, 25 kilometers far from Ilakaka. One of quote headlight of sapphires production. The higher edges of rivers abound in sapphires, chrysoberyls, etc. Here in area of Vohimena vaovao. The sandstones, fragile, have been knife cut by river. SANDSTONES of ISALO The base of group of Isalo is entirely continental. Sometimes significant marine incursions and of long duration were introduced into medium and higher parts. The group of Isalo begins at top from lower Triassic and continues until end of Jurassic means. One separates there: Isalo I, at base, especially sandy, continental. Isalo II, argilo - sandy with some marine intercalations. Isalo III, argilo - sandy with side passage to great marine formations. The essential characteristic of Isalo formations is their main constitution of soft sandstones, very permeable, badly cemented which disaggregate easily on surfaces by giving thick siliceous sand coverings. The porous nature of sandstones constitutes an excellent tank which stores water of rains to restore it during dry season. · Sakalama, 60 kilometers south from Ilakaka. MADAGASCAN CORUNDUMS At back, ruiniform sandstones of Isalo range. GGGEMS.COM
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¦ Madagascar Safari ¦ Madagascar Safari 2 ¦ Pakistan Gem Safari ¦ Sakalama ¦
Madagascar GarnetsWritten by Alain Darbellay GGGems
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right left Deltoid dodecahedron Pentagonal tetraedrical dodecahedron . Almandine in matrix Spessartite (Ambohimarangitra) Malaya (Andoharano) Malaya (Madagascar) Rhodolite (Ankilytokana) Hessonite (Soakibany) Imperial Malaya (Madagascar) In Madagascar, one finds rhodolite in a gneiss rich in biotite, in which (almandite-pyrope) is presented in form of small grains, or with state of large porphyroblasts, generally deprived of geometrical contours, plagioclase (oligoclase with andesine) is feldspar dominating and sometimes exclusive. These gneisses contain sometimes pegmatic beds very rich in crystals. One very finds also garnetiferous gneisses containing little biotite, hardly directed. Kinzigites. The gneisses which have been just enumerated have a very clear schisteous structure, which had with biotite abundance. A rather frequent type is approximately blocks and presents a compact aspect, thanks to prevalence of large garnets without geometrical form, associated quartz and feldspar granoblastic, biotite is not very abundant. The structure points out that of corneal micaceous of contact of granite. This gneiss can be compared with kinzigite of Black Forest. Leptynites with amphibolo-pyroxenite intercalation rich in garnets of a pale pink (almandite-pyrope), with often rutile and graphite abound in certain areas of Madagascar. The feldspar is orthoclase, associated with ogigoclase-albite feldspar and sometimes with spindle-shaped microperthite, there exists much of myrmekite. These rocks are with fine grins, but they very often contain large regularly distributed crystals. Usually garnet does not have a geometrical form, but it takes clear faces in more quartzose zones. Leptynites derive from granites by disappearance of mica; garnetiferous mica schists constitute opposed pole in which biotite prevails, with progressive disappearance of feldspar. The Besafotra river carry out spessartites on several kilometers from their source, doubtless a sodolitic pegmatite. A walk of 25 kilometers among mountains is necessary to reach this place. SPESSARTITE GARNET The tanety "grounds bordering river," are also object of orange garnet's fever. Sifting in river. Initially, spessartite appeared in Besafotra river, searched out here near to its source. Ankilytokana, one of fabulous rhodolite occurrences exploited in a leptynite vein on a sixteen meters depth. RHODOLITE GARNET Leptynites are primarily consisted in alkaline feldspars and quartz. When these rocks are not ribboned, and that is frequent, it is often difficult to decide if a sample, not seen in place, belongs to a leptynite or an aplite, it should be noticed that in Madagascar, these last contain microcline and not of orthoclase. In this area, one observes graphite spangles in leptynites. Malaya garnet discovered into September 1998, in eluvium in a broken up leptynite. The modest depth of deposit did not require a significant work to extract it. This stone shows an exceptional capacity to restore light, thanks in particular to its high refractive index, especially under not very enlightened condition. Malaya Garnet Discovery Cutting Styles¦Characteristics¦ Crystalline Systems ¦ Madagascar Sapphire ¦ Corundum data ¦ Malaya Garnet ¦ Rhodolite Garnet ¦ Spessartite Garnet ¦ Hessonite Garnet ¦
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