|
| |
| (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. |
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|
Occurences:
In the acid magmatic rocks and associated |
| pegmatites,
limestones and schists, placers. |
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| 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 |
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|
 1 |
 2 |
 3 |
 4 |
 |
|
Fig. 1& 2 : Triangular
type |
Fig. 3 & 4 :Hexagonal
type |
Very
rare type of |
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|
Rubellite from Antsongombato |
tourmaline:
white head |
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and
red body. |
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5 |
 |
 6 |
 |
| Crystal
of the hexagonal type finished |
Polychrome
tourmaline
being in Tsilaizina, 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. |
| |
 |
|
 |
 |
| 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 |
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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 ( 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 |
|
|
| occurrence
was famous for its red-ruby
tourmalines. |
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 |
|
Your
guide to GGGems |
 |
All of the pictures on this
website have been shot by
gggems.com |
Alain
Darbellay |
|
Text written by Alain Darbellay. |
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|
