Ilakaka Madagascar ( Sapphire rush )

Written by Alain Darbellay GGGems

© 2004 All rights reserved. ILAKAKA · The plateau of Ilakaka in 1992. Ilakaka is located onrepparttar road to Tulear, south-west of Madagascar. The discovery of sapphire inrepparttar 109302 current of 1998 transformedrepparttar 109303 area. · Ilakaka in 1999. It is inrepparttar 109304 accesses ofrepparttar 109305 downwards brook named Ilakaka thatrepparttar 109306 first sapphires were found in 1998. The existence of gemmiferous minerals, including corundum was known for a long time inrepparttar 109307 sandstones of Isalo. French geologists having undertaken research in 1946 in particular. If their discovery did not cause particular interest atrepparttar 109308 time, several reasons can be advanced : repparttar 109309 political instability which reigned afterrepparttar 109310 second world war inrepparttar 109311 colony, andrepparttar 109312 fact thatrepparttar 109313 majority of corundums coming fromrepparttar 109314 area of Ilakaka must be heated to be marketed, indeed, a blue stone, but cloudy, could not inevitably let suppose to its discoverers that it would become pure and transparent after a suitable heat treatment. Moreover, knowledge in this field remained summary at that time. In Ilakaka,repparttar 109315 arrival of merchants coming from Thailand and from Sri-Lanka changed things, because this group of purchasers became experts in "the " Tsy misy mandronono, tsy misy prix" enhancement of corundum." Thus,repparttar 109316 cloudy stones of This sentence is none by everyone in better quality will be often sold as (untreated Sri-Lankan Ilakaka. sapphires) onrepparttar 109317 international market, this because of It means that : " ifrepparttar 109318 stone is not milky,repparttar 109319 difficulties in detecting heating treatment in a stone its owner will not get price for it." from Ilakaka not containing other inclusion only one haze of fine titanium drops, reabsorbed after heating. ( Note: that true untreated Sri-Lankan sapphires are rare.) The excavations followrepparttar 109320 gravel deposits whichrepparttar 109321 Impressing holes borerepparttar 109322 sandstones of Madagascans call lalam' bato, (the way of stones.) Ilakaka testifying torepparttar 109323 fever of sapphire. Ankaboka, one ofrepparttar 109324 many gemmiferous places ofrepparttar 109325 area. · Maromiandry is located The sivany (sifting of gravels) in Maromiandry. 40 kilometers north ofrepparttar 109326 Seldom practiced dry as in this place distant trunk road between from a river. Ilakaka and Sakaraha. The sifting of gemmiferous gravels in river close to Maromiandry.

Madagascar Garnets

Written by Alain Darbellay GGGems

© 2004 All rights reserved.

Crystalline System: cubic. Red - violetish: Hardness Density Ref.Index Pyrope Mg3Al2Si3O12 7,25 3,58 g / cm3 1,714 Almandine Fe3Al2Si3O12 7,50 4,32 1,830 Rhodolite Mg,Fe3Al2SiO12 7,25 3,78 - 3,90 1,74-1,78 Orange - yellow-brown : Spessartite Mn3Al2Si3O12 7,25 4,20 - 4,25 1,78 - 1,81 Malaya Mn3Al2(SiO4)3 7,25 3,74 - 4,00 1,78 Hessonite Ca3Al2(SiO4)3 7,25 3,58 - 3,65 1,73 - 1,74 Green : Tsavolite Ca3Al2(SiO4)3 7,25 3,60 - 3,68 1,73 - 1,74 Uvarovite Ca3Cr2Si3O12 7,50 3,85 1,87 Dementoïde Ca3F2SiO12 6,5 - 7 3,82 - 3,85 1,89

In a perfect crystal, when a face appears inrepparttar crystal inrepparttar 109301 process of growth, allrepparttar 109302 faces appear withrepparttar 109303 same development. If one ofrepparttar 109304 symmetrical faces is less developed on a crystalline sample, or exceptionally does not appear, that comes fromrepparttar 109305 accidental actions ofrepparttar 109306 external environment which opposed its growth. Temperature, pressure, nature ofrepparttar 109307 mineral solution, speed ofrepparttar 109308 crystalline growth andrepparttar 109309 direction ofrepparttar 109310 movement of solution etc... representrepparttar 109311 external influences onrepparttar 109312 crystalline forms. The frequency ofrepparttar 109313 faces ofrepparttar 109314 crystals is related torepparttar 109315 reticular density,repparttar 109316 fast growth of some faces influencesrepparttar 109317 crystalline form definitively. Garnet thus crystallizes underrepparttar 109318 cubic system, whose crystals are characterized byrepparttar 109319 presence of three quaternary axes A4 joiningrepparttar 109320 centers ofrepparttar 109321 faces, four ternary axes A3 joiningrepparttar 109322 opposed tops, six binary axes A2 joiningrepparttar 109323 mediums ofrepparttar 109324 edges. · One ofrepparttar 109325 causes modifyingrepparttar 109326 initial form of crystals is truncation. Truncation on corners. Cube Dodecahedron Truncation cuts two different lengths on adjacent corners. Cube Tetrahexahedron Truncation cutting three equal lengths out ofrepparttar 109327 three adjacent corners. Cube Octahedron Truncation cuts two equal lengths out of two corners and a larger length onrepparttar 109328 third. Trisoctahedron Octahedron Truncation onrepparttar 109329 segment crosses, two equal lengths out of two corners, a smaller length onrepparttar 109330 third.

Cube Trapesohedron Octahedron Trapesohedron Dodecahedron Trapesohedron Hexoctahedron Dodecahedron Almandine in matrix Pyrope-Almandine Almandine in matrix Almandine in matrix Almandine in matrix Rhodolite (Ambohitompoina) There is also a law according to which certain crystals do not present modifications that on half of corners, or ofrepparttar 109331 similar angles. Here is a truncation on a top cutting three different lengths on corners, and which repeats only three times around repparttar 109332 ternary axis. Cube and diplohedron Diplohedron Right Gyrohedron Left Gyrohedron The diplohedron is made of twenty-four irregular quadrilaterals. The class plagiohedron whose faces (HKL) are arranged inrepparttar 109333 spiral order. In other cases, twelve irregular pentagons are formed by a truncation on one sharp angle, on both adjacent angles,repparttar 109334 unequal lengths, it isrepparttar 109335 pentagonal dodecahedron. Positive Negative Almandine in matrix Tsavolite (Madagascar) Spessartite in pegmatite (Tsilaizina)

The regular tetrahedron consisted four equilateral triangles forming between them an angle of 70° 31. Positiv tetrahedron Négativ tetrahedron Octahedron Positiv tetrahedron Cube The tetrahedron or triakistetrahedron consisted twelve faces which are isosceles triangles, andrepparttar 109336 hexatetrahedron with its twenty four triangular faces. Triakistetrahedron Hexakistetrahedron The trapezoidal dodecahedron consisted twelve quadrilaterals deltoid andrepparttar 109337 tetrahedral pentagonal dodecahedron are formed by a truncation appearing on each top and cutting three different lengths on angle.

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