Madagascar Tourmaline - Career Article

By:Alain Darbellay GGGems

© 2004 gggems.com All rights reserved.

(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
Refractive index: 1.62 - 1.64

· Chemical Properties: Alumina borosilicate with fluorine.

Occurences: 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
Crystal of the hexagonal type finished Polychrome tourmaline being in Tsilaizina, 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 SLICED TOURMALINE
of a complete crystal cut tourmaline sliced in section from Vohitrakanga.
parallel to the ternary
axis.

Rubellite Chrome Tourmalines Indigolite from Anjahamiary. 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 century. The attack Mine of Alakamisy Itenina ( Fianarantsoa area).
measured about fifteen meters, the coal face was to This mine is worked in alluvium, the first stones were
hillside 10 meters above the brook, it showed the discovered in 1989 in a rice plantation. It produced
presence of a large sill of hard pegmatite, laid out in rubellites and remarkable tourmalines with geometrical
benches lities by a secondary cleavage. To the wall drawings.
one 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 elluvial.

¦ Cutting Styles ¦ Characteristics ¦ Crystalline Systems ¦ Madagascar Sapphire ¦

¦ Tourmaline Polychrome ¦ Tourmaline Crystal ¦ Tourmaline Crystal 2 ¦ Tourmaline Slice ¦

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