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.

Madagascar gem safari

Written by Alain Darbellay GGGems

© 2004 All rights reserved. MADAGASCAR GEM SAFARI 2 Sapphire from Maromby in a metamorphic limestone. ( Andranondambo area.) Looking for sapphire onrepparttar ground in 1992. Sapphires from Andranondambo, discovered in 1991. ( South-East of Madagascar ) In 1658, Flacourt,repparttar 109300 governor of Fort-Dauphin mentions sapphires inrepparttar 109301 south of Madagascar. In 1808, Barthélemy Hugon writes that inrepparttar 109302 valley of Ambolo there is a so beautiful stone and so rare that lapidaries have not been able to recognize it and it was above of all that is not diamond. ... In 1991, atrepparttar 109303 time of repparttar 109304 great dryness inrepparttar 109305 south, sapphire samples are found, several centuries after their first discovery. The son of Mrs. Dauphine, innkeeper in Tranomaro, main village ofrepparttar 109306 valley, was amongrepparttar 109307 prospectors. Actually, one ofrepparttar 109308 most beautiful quality inrepparttar 109309 world is just leaving ground. The area of Tranomaro is characterized by an extreme calcic and magnesian paragneiss abundance: gneiss with diopside, plagioclasites, pyroxenites, wernerites, wolastonite limestones, with varied leptynites, generally with garnet, kinzigites, quarzites. One finds there rather frequently syenitic gneisses or lamboanites. Gneisses of injection are very frequent. The typomorphic minerals are: basic diopside, scapolite, calcite, plagioclases, wollastonite, garnet, cordierite and corundum. East of Tranomaro, arteritic and eyesys injections assign gneisses at leptynites. Cordierite gneiss bands are deeply injected bed by bed,repparttar 109310 injection has introduced magnetite in abundance. Wollastonites form ptymatic lenses with Marohotro, 18 km. south from Andanondambo. folds very tortured atrepparttar 109311 middle ofrepparttar 109312 limestone. Note: The sapphire onrepparttar 109313 left comes from Ambandanira, and aluminous anorthites or sakenites. that on right-hand side from Maromby (area of Andranondambo) Sapphire from Behataza plateau (Andranondambo area) Sapphires from Ilakaka. One ofrepparttar 109314 various holes in sandstone forming ( South-West of Madagascar )repparttar 109315 deposit of Ilakaka discovered in to 1998. Blue sapphires , pink and violet, Ilakaka area. SANDSTONES OF ISALO. The white sandstones of Isalo present imposing stratifications intersected with gravel beds and small conglomerates. These soft sandstones resisted to erosion and taken a ruiniform relief becauserepparttar 109316 presence of braces siliceous veins. The mineral-bearing deposits include : a deposit of generally classified gravels,repparttar 109317 richest part and larger elements being atrepparttar 109318 base ofrepparttar 109319 bed - rock. MORE ABOUT ILAKAKA

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