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(Na,
Li,Ca) (Fe2,
Mg, Mn, Al)3
Al6 I(OH)4 I
(BO3)3ISi6O18I |
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Crystallographic
properties: Trigonal. |
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Hardness
7-7.5 Density 3.02 to 3.26 |
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Chemical
Properties: Alumina borosilicate with fluorine. |
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Deposits:
In the acid magmatic rocks and associated |
pegmatites,
limestones and schists, placers. |
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Coloured
tourmalines are related to sodolithic pegmatites. |
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One
distinguishes two principal types of tourmalines: the hexagonal type and
the triangular one. |
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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 |
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Bi-terminated, one
finds with the one of the ends of the ternary axis the rhomboèdre |
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R,
and with the other same
the rhomboèdre combined with that (0111) = P. |
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The
triangular type, here is never finished at the two ends, it is
characterized by |
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the
prevalence
of faces I in the prismatic zone, while those S are very
narrow just as |
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those S2
which
accompany them. The crystals on the finished end carry the base C, |
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combined with the
rhomboèdre R; in the same way sometimes with the rhomboèdre P
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and the base C |
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1 |
2 |
3 |
4 |
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Fig. 1& 2 : Triangular
type |
Fig. 3 & 4 :Hexagonal
type |
Very
rare type of |
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Rubellite from Antsongombato |
tourmaline:
white |
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head
and
red body. |
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5 |
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6 |
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Crystal
of the hexagonal type finished |
Polychrome
tourmaline being in Tsilaisina, Madagascar. |
at
a peak frequently found in Tsilaisina. |
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Liddicoatite Tourmaline |
Deep-PinkTourmaline |
Blue-greenTourmaline. |
Indigolite |
from Anjanabonoina. |
Antsongombato type. |
(
Kunar valley, Afghanistan.) |
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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. |
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Diagrammatic
provision
Growth zoning and geometrical drawings in a |
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of
a complete crystal cut
tourmaline
sliced in section from Vohitrakanga. |
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parallel
to the ternary axis. |
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Rubellite |
Chrome Tourmalines |
Indigolite from
Anjamiary |
Macle of green
tourmaline |
Antsongombato type. |
from Tsaniria. |
( Madagascar ) |
Estaknala ( Pakistan ) |
( Madagascar ) |
( Madagascar ) |
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Sketch
of the Antsongombato mine |
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( 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 |
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sees a schistous limestone greenish and broken |
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up,
to
the roof, one distinguishes only clay. |
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This
deposit
was famous for its red-ruby tourmalines. |
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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. |
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All of
the pictures on this site have been shot by Darbel du Bourg. |
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