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(Na, Li,Ca) (Fe2, Mg, Mn, Al)3 Al6 I(OH)4 I (BO3)3ISi6O18I
· Crystallographic properties: Trigonal.
Hardness 7-7.5 Density 3.02 to 3.26
· Chemical Properties: Alumina borosilicate with fluorine.
   Deposits: 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 rhomboèdre 
R, and with the other same the rhomboèdre 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 rhomboèdre R; in the same way sometimes with the rhomboèdre 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            
Crystal of the hexagonal type finished        Polychrome tourmaline being in Tsilaisina, Madagascar.
at a peak frequently found in Tsilaisina.
 
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.
  
Diagrammatic provision              Growth zoning and geometrical drawings in a
of a complete crystal cut            tourmaline sliced in section from Vohitrakanga.
parallel to the ternary axis.
   Rubellite   Chrome Tourmalines Indigolite from Anjamiary Macle of green tourmaline
   Antsongombato type.   from Tsaniria. ( Madagascar )   Estaknala ( Pakistan )
  ( Madagascar )   ( Madagascar )
Sketch of the Antsongombato mine  
( Antsirabe area) at the beginning of the 20th   Mine of Alakamisy Itenina ( Fianarantsoa area).
century. The attack measured about fifteen   This mine is worked in alluvium, the first stones were
meters, the coal face was to hillside 10 meters   discovered in 1989 in a rice plantation. It produced
above the brook, it showed the presence of a   rubellites and remarkable tourmalines with geometrical
large sill of hard pegmatite, laid out in benches   drawings.
lities by a secondary cleavage. To the wallone      
sees a schistous limestone greenish and broken 
up, to the roof, one distinguishes only clay. 
This deposit was famous for its red-ruby tourmalines.
        
                  The Mine of Anjanabonoina, located in the high plateaus, 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 eluvial.
                  
All of the pictures on this site have been shot by Darbel du Bourg.
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