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Tourmaline
A study of  MADAGASCAR TOURMALINE
(Na, Li,Ca) (Fe2, Mg, Mn, Al)3 Al6 I(OH)4 I (BO3)3ISi6O18I Tourmaline mineral, red Madagascar tourmaline, exclusive tourmalines, tourmaline information data
Tourmaline crystallographic properties: Trigonal.
Hardness 7 - 7.5 
Density 3.02 to 3.26
Refractive index: 1.62 - 1.64
Chemical Properties: Alumina borosilicate with fluorine.
   Occurrences: In the acid magmatic rocks and associated
                         pegmatites, limestones and schists, placers.
Coloured tourmalines are related to sodolithic pegmatites.
One distinguishes two principal types of tourmalines: the hexagonal type and the triangular one.
The hexagonal type is especially characterized by the presence, in the prismatic zone, of 
the well developed S1 faces, and those of L always narrow. When the crystals Bi-terminated, 
one finds with the one of the ends of the ternary axis the rhomboedron R, and with the other
same the rhomboedron combined with that (0111) = P.
The triangular type, here is never finished at the two ends, it is characterized by the
prevalence of faces I in the prismatic zone, while those S are very narrow just as those S2
which accompany them. The crystals on the finished end carry the base C, combined with
the rhomboedron R; in the same way sometimes with the rhomboedron P and the base C
1 2 3 4
         Fig. 1& 2 : Triangular type          Fig. 3 & 4 :Hexagonal type Very rare type of
         Rubellite from Antsongombato tourmaline: white head
  and red body.
         5         6             Tourmaline crystal, red white Madagascar tourmaline, exclusive tourmalines, tourmaline information data
Crystal of the hexagonal type finished        Polychrome tourmaline being in Tsilaizina, Madagascar.
at a peak frequently found in Tsilaisina.
 
Liddicoatite Tourmaline crystal, red brown white Madagascar tourmaline, exclusive tourmalines, tourmaline information data Tourmaline crystal, red pink Madagascar tourmaline, exclusive tourmalines, tourmaline information data Tourmaline crystal, blue green Afghanistan tourmaline, exclusive tourmalines, tourmaline information data Tourmaline crystal, blue Afghanistan tourmaline, exclusive tourmalines, tourmaline mineral information data
Liddicoatite Tourmaline                   Deep-PinkTourmaline  Blue-greenTourmaline.          Indigolite
from Anjanabonoina.                   Antsongombato type.          (  Kunar valley, Afghanistan.)
Colors of tourmalines: Blue is due to bivalent iron, (magnesium gives a clearer blue) the manganese produce tone
from pink to red, chromium and vanadium is in green tourmalines, the yellow and the brown one is produced by
trivalent iron.
  
Polychrome Tourmaline cabochon, red white green Madagascar tourmaline, exclusive tourmalines, tourmaline information data Polychrome Tourmaline cabochon, red white green Madagascar tourmaline, exclusive tourmalines, tourmaline information data Multicolor Tourmaline cabochon, red white green blue Madagascar tourmaline, exclusive tourmalines, tourmaline information data
 Cabochon ribboned tourmalines
Watermelon Tourmaline slice, red white green pink Madagascar tourmaline, exclusive tourmalines, tourmaline information data
Diagrammatic provision of a complete crystal cut parallel to the ternary axis. Growth zoning and geometrical drawings in a tourmaline sliced in section from Vohitrakanga. SLICED TOURMALINE
           
   
           Tourmaline crystal containing multicolored geometric patterns weighting 7.5 kilos.  
Discover:

The Ribboned Tourmaline !

and its Colors.

Rubelite Tourmaline crystal, red Madagascar tourmaline, exclusive tourmalines minerals, tourmaline information data Chrome Tourmaline crystal, green Madagascar tourmaline, exclusive tourmalines, tourmaline information data Indicolite Tourmaline crystal, blue Madagascar tourmaline, exclusive tourmalines, tourmaline information data
   Rubellite   Chrome Tourmalines   Indigolite from Anjamiary.     Macle of green tourmaline
   Antsongombato type.   from Tsaniria. ( Madagascar )     Estaknala ( Pakistan )
  ( Madagascar )   ( Madagascar )
Rubellite from Antsongombato:
The crystals of this remarkable mineral are very variable in size, small one are homogeneous only and of a beautiful pigeon blood red color lighter or darker. Those larger almost always have a complex structure and are formed by concentric zones. At the time of the deposit discovery, very large crystals were quite exceptional and were still inhomogeneous.
In some rubellites, alternating zones are all colored in red, more or less vivid, the center is such an intense purplish red, middle and peripheral zones are red or pink in various shades and even colorless. In other stones the center is composed of yellow or brown, and the periphery composed by rubellite. The reverse also occurs on large crystals that appear black while the central parts show of a beautiful red.
When color zoning are numerous they are very thin. The optical properties of tourmaline from Antsomgombato examined on blood-red pieces, lighter red and zoned crystals show that they are all slightly biaxial.

In Tsilaisina, zoned crystals are also very common. Some crystals show some zones of alternating color and which are not concentric, but arranged in parallel layers over the height of the prism. Here pink tourmaline is distinguished from others by its low content of manganese and a high proportion of lime.

The main fact that emerges from the observation of tourmalines from
the above occurrences, is their undeniable relationship. All tourmalines contain manganese in varying proportions, and sometimes substantial, all are of a remarkable poverty in magnesia and iron oxide with the exception of black tourmaline. The silica and alumina will undergo changes that reach only 2%, and the total amount of alkali is between 1.04 and 3.48%. Fluoride, always constant, oscillating between 1.4 and 0.73% boric acid and between 9.46 and 11.03%. The most alcaliferous tourmaline is the red of Antsongombato, 3.48%. The alkalies do not seem to have a direct influence on the coloration. Here, manganese is probably the main chromogenous factor, but the color also depends on the elements that accompany it. The combined presence of lime appears to be the cause of the pink or red.
Sketch of the Antsongombato mine ( Antsirabe area)
at the beginning of the 20th century. The attack Mine of Alakamisy Itenina ( Fianarantsoa area, 
measured about fifteen meters, the coal face was to Madagascar).
hillside 10 meters above the brook, it showed the This mine is worked in alluvium, the first stones were
presence of a large sill of hard pegmatite, laid out in discovered in 1989 in a rice plantation. It produced
benches lities by a secondary cleavage. To the wall rubellites and remarkable tourmalines with geometrical
one sees a schistous limestone, greenish and broken up, drawings.                             Image J. Darbellay
to the roof, one distinguishes only clay. This
occurrence was famous for its red-ruby tourmalines.
        
Anjanabonoina Tourmaline mine, red pink Madagascar tourmalines, exclusive tourmalines, tourmaline information data
                The Mine of Anjanabonoina, located in the highlands of Madagascar, produced rubellites
                green tourmalines, brown-orange, pink, blue-sky, purple, and a variety of rare stones since   
                the end of the 19th century.
                This deposit is elluvial.
  Cutting Styles Characteristics Crystalline Systems Madagascar Sapphire
Tourmaline Polychrome Tourmaline Crystal  Tourmaline Crystal 2 Tourmaline Slice
   
 
   
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All of the pictures on this website have been shot by gggems.com Alain Darbellay
     Text written by Alain Darbellay.
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