Madagascar,corundums,amp,#40,S education Madagascar corundums ( Sapphire & Ruby discovery

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© 2004 gggems.com All rights reserved. AL2O3 Sapphire found in a metamorphized limestone. · Crystallographic properties of corundum: Trigonal.c = 1,3630 pp 0 86°4' ; pa1 = 122°26' Macle according to p (1011), often polysynthetic, accompanied by plans of separation, similar plans are also observed according to a1 (0001) unequal break to conchoïdal. Hardness 9. Density 3,95 to 4,1 Refractive index: 1.76 - 1.77 Uniaxial and optically négative.ng = 1,7675; Np = 1,7593 The faces a1 frequently show the phenomenon of asterism, generally due to reflexions within separation p. Strong polychromatism , with following maximum ng. · Chemical properties: corundum is composed of pure alumina; its colouring is due to metallic oxide traces or inclusions. The color of sapphire, due to iron and titanium oxide, gives its best effect under daylight. Electric light makes it often dark. The color of the ruby, due to chromium oxide, on the contrary shows its most luminous red under electric lighting. The Corundum shows in Madagascar two different aspects: 1 stony and opaque crystals. 2 crystals of smaller size often transparent and usable as gem. In Madagascar, stony corundum comes from mica schists metamorphized by granite, as well as granitic veinules endomorphized and more or less deprived of quartz which injects those. Silimanite is a usual satellite of corundum in this type of deposit. One also finds some in eruptive rocks, syenites. Gems are generally found in alluvium, but come either from basaltic slags, or from metamorphized limestones or endomorpheous feldspatic rocks. 1 2 3 4 5 One distinguishes two principal types of corundum in Madagascar: Type I : isoceloedric, more or less acute accompanied or not by a small face a1 (0001) and more rarely by facets p (1011). Represented by figures 1 to 11, but which often become complicated in consequence of the irregularity of the development of some of their faces and by stacking with parallel axes of a great number of individuals. 6 7 8 9 10 11 12 13 Scalenoedron Stacking with parallel axes, Crystal supporting on one of its bases gutters at contours of the face. a small rhombohedron p in parallel position. Type 2: Characterized by the association of the prism d 1 (1120) at a broad base, with which can associate the isosceles ones, among which e 3 is most frequent, as well as the rhombohedron p. The base of Malagasy corundum crystals very frequently shows scratches or triangular figures in relief, limited by p. Macle of blue corundum. Translucent violet - pink sapphire Ruby in amphibolite. The crystals engaged in rocks, rich in mica have rough faces, encrusted of biotite or muscovite, minerals which also exist at the state of inclusions, associated with magnetite and pyrite. Because of its hardness, its inalterability and its density, corundum constitutes a standard mineral of alluvia. Ruby Giant Sapphire in a metamorphic dolomitic limestone. Polychrome Sapphire Blue Sapphire ( origin: Blue Sapphire ( origin: Ilakaka 1999 ) ( origin: Iankaroka 1990 ) Andranondambo 1992 ) Found in the sandstones of Isalo in This sapphire comes from a granit, The stone comes from alluvium, the shape is rounded. its shape is intact. a metamorphized limestone. The origin of the stone is a limestone. · The structure of crystals. It is R.J.Haüy who put forth the first assumption, confirmed 200 years later, on the structure of the crystallized material. He lets drop accidentally a calcite crystal which broke into small rhomboedrons. He supposed whereas the crystals were consisted of stacking small rhomboedrons elementary (that he called the "integral molecule"), he could reconstitute all known shapes of calcite. In a crystal lattice, three atoms or groups of atoms (nodes), which is not on the same line, determine a plan called reticular plan. But there is a great number of these plans: it is enough to choose nodes not strictly nearby. As the network is infinite, there is even an infinity of possible plans. The dimension of the faces does not play of role. In the course of growth, a face can develop more quickly than another. The angle that the faces make between them remains constant, since it depend on the network. This structure of the crystalline material explains the law of the constancy of the dihedral angles. Triangular figure on a Scratches on a rare Stacking in macle Triangles on a translucent colorless corundum. colorless corundum. of a ruby. corundum. Triangular figure on a Triangles in step on a blue Remarkable macle of blue corundum. corundum from Maromby. red corundum. Sapphire & Ruby Safari Gem ruby from Ambatovaravarana. The alluvial ruby deposit of Ambatovaravarana in the high plateaus, is in the left center on the picture, under the hill. Macle of blue sapphire. Macle of ruby 60 grms. Information ¦ Cutting Styles ¦ Characteristics ¦ Crystalline Systems ¦ Madagascar Sapphire Andranondambo Sapphires ¦ Blue Sapphire Crystal ¦ Ruby Crystal ¦ Sapphire Slice Your guide to GGGems.com All the pictures on this site have been shot by gggems.com Alain Darbellay © 1987 - 2004 gggems.com All rights reserved.