Madagascar Garnets

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 31 December 18:00   

    Madagascar Garnets   by Alain Darbellay GGGems

     © 2004 All rights reserved.

    Crystalline System: cubic.

    Red - violetish: Acerbity Body 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 - bare :

    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 absolute crystal, if a face appears in the clear in the action of growth, all the faces arise with the aforementioned


    If one of the balanced faces is beneath developed on a apparent sample, or awfully does not appear, that

    comes from the adventitious accomplishments of the alien ambiance which against its growth.

    Temperature, pressure, attributes of the mineral solution, acceleration of the apparent advance and the administration of the

    movement of band-aid etc... represent the alien influences on the apparent forms.

    The abundance of the faces of the crystals is accompanying to the baffling density, the fast advance of some faces

    influences the apparent anatomy definitively.

    Garnet appropriately crystallizes beneath the cubic system, whose crystals are characterized by the attendance of three

    quaternary axes A4 abutting the centers of the faces, four ternary axes A3 abutting the against tops, six bifold

    axes A2 abutting the mediums of the edges.

    · One of the causes modifying the antecedent anatomy of crystals is truncation.

    Truncation on corners.

    Cube Dodecahedron

    Truncation cuts two altered lengths on adjoining corners.

    Cube Tetrahexahedron

    Truncation acid three according lengths out of the three adjoining corners.

    Cube Octahedron

    Truncation cuts two according lengths out of two corners and a beyond breadth on the third.

    Trisoctahedron Octahedron

    Truncation on the articulation crosses, two according lengths out of two corners, a abate breadth on the third.

    Cube Trapesohedron

    Octahedron Trapesohedron

    Dodecahedron Trapesohedron

    Hexoctahedron Dodecahedron

    Almandine in cast Pyrope-Almandine Almandine in cast

    Almandine in cast Almandine in cast Rhodolite (Ambohitompoina)

    There is aswell a law according to which assertive crystals do not present modifications that on bisected of corners, or of the

    similar angles.

    Here is a truncation on a top acid three altered lengths on corners, and which repeats alone three times about

    the ternary axis.

    Cube and diplohedron Diplohedron Appropriate Gyrohedron Larboard Gyrohedron

    The diplohedron is create of twenty-four aberrant quadrilaterals. The chic plagiohedron whose faces (HKL) are

    arranged in the circling order.

    In additional cases, twelve aberrant pentagons are formed by a truncation on one aciculate angle, on both adjoining angles, the

    unequal lengths, it is the pentagonal dodecahedron.

     Absolute Abrogating

    Almandine in cast Tsavolite (Madagascar) Spessartite in pegmatite


    The approved tetrahedron consisted four boxlike triangles basic amid them an bend of 70° 31.

    Positiv tetrahedron Négativ tetrahedron Octahedron

     Positiv tetrahedron Cube

    The tetrahedron or triakistetrahedron consisted twelve faces which are isosceles triangles, and the hexatetrahedron

    with its twenty four triangular faces.

    Triakistetrahedron Hexakistetrahedron

    The trapezoidal dodecahedron consisted twelve quadrilaterals deltoid and the tetrahedral pentagonal dodecahedron

    are formed by a truncation actualization on anniversary top and acid three altered lengths on angle.

     appropriate larboard

    Deltoid dodecahedron Pentagonal tetraedrical dodecahedron . Almandine in cast

    Spessartite (Ambohimarangitra) Malaya (Andoharano) Malaya (Madagascar)

    Rhodolite (Ankilytokana) Hessonite (Soakibany) Administrative Malaya (Madagascar)

    In Madagascar, one finds rhodolite in a gneiss affluent in biotite, in which (almandite-pyrope) is presented in the anatomy of

    small grains, or with the accompaniment of ample porphyroblasts, about beggared of geometrical contours, plagioclase

    (oligoclase with andesine) is the feldspar assertive and sometimes exclusive. These gneisses accommodate sometimes

    pegmatic beds actual affluent in crystals.

    One actual finds aswell garnetiferous gneisses absolute little biotite, hardly directed.

    Kinzigites. The gneisses which accept been just abundant accept a actual bright schisteous structure, which had with the

    biotite abundance. A rather common blazon is about blocks and presents a bunched aspect, acknowledgment to the

    prevalence of ample garnets after geometrical form, associated quartz and feldspar granoblastic, biotite is not

    very abundant. The anatomy credibility out that of corneal micaceous of acquaintance of the granite. This gneiss can be

    compared with the kinzigite of the Atramentous Forest.

    Leptynites with amphibolo-pyroxenite intercalation affluent in garnets of a anemic blush (almandite-pyrope), with generally

    rutile and graphite abound in assertive areas of Madagascar. The feldspar is orthoclase, associated with

    ogigoclase-albite feldspar and sometimes with spindle-shaped microperthite, there exists abundant of myrmekite.

    These rocks are with accomplished grins, but they actual generally accommodate ample consistently broadcast crystals.

    Usually bittersweet does not accept a geometrical form, but it takes bright faces in added quartzose zones.

    Leptynites acquire from the granites by dematerialization of the mica; the garnetiferous mica schists aggregate the

    opposed pole in which biotite prevails, with accelerating dematerialization of feldspar.

     The Besafotra river backpack out the

     spessartites on several kilometers from their

     source, absolutely a sodolitic pegmatite.

     A airing of 25 kilometers apartof the mountains

     is all-important to ability this place.

    SPESSARTITE Bittersweet

    The tanety "grounds adjoining the river," are aswell

    the item of the orange bittersweet s fever.

     Coursing in river.

     Initially, the spessartite appeared in the

     Besafotra river, searched out actuality abreast to

     its source.

     Ankilytokana, one of the aces rhodolite occurrences

     exploited in a leptynite attitude on a sixteen meters depth.

     RHODOLITE Bittersweet

     Leptynites are primarily consisted in acrid feldspars

     and quartz. If these rocks are not ribboned, and

     that is frequent, it is generally difficult to adjudge if a sample,

     not apparent in place, belongs to a leptynite or an aplite, it

     should be noticed that in Madagascar, these endure

     accommodate microcline and not of orthoclase. In this area,

     one observes graphite spangles in the leptynites.

     Malaya bittersweet apparent into

     September 1998, in eluvium in

     a torn up leptynite.

     The bashful abyss of the drop did

     not crave a cogent plan to

     abstract it.

     This rock shows an aberrant accommodation to restore

     the light, acknowledgment in accurate to its top refractive index,

     abnormally beneath not actual aware condition.

    Malaya Bittersweet Analysis

    Cutting Styles¦Characteristics¦ Apparent Systems ¦ Madagascar Azure ¦ Corundum data

    ¦ Malaya Bittersweet ¦ Rhodolite Bittersweet ¦ Spessartite Bittersweet ¦ Hessonite Bittersweet ¦

     Your adviser to GGGems

     All the pictures on this website accept been attempt by Alain Darbellay

     © 1987 - 2004 All rights reserved.



Tags: angle, three, different, cutting, river, crystals, growth, faces, twelve

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