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A
study of MULTICOLOR TOURMALINE
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Discover:
The
Ribboned Tourmaline ! |
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Tourmaline,
mixed crystals of aluminium boron silicate with a |
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complex
and changing
composition, shows
a
variety of colors
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and designs may be unique in gemstones. |
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The mine of
Alakamisy Itenina in the highlands of Madagascar, |
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was discovered in
1989 in a rice plantation. |
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The tourmaline
deposit is alluvial and the shape of the stones |
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remains
rolled. |
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This occurrence is
hand worked and the
stones are at
a depth |
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ranging
from a few meters up to twelve meters. |
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©
Image J. Darbellay |
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Atomic
Bonding.
In
minerals, atoms bind together to form molecules through their orbital of
higher energy, i.e. that only the outer layers of electrons involved. They
are the ones who also, by electromagnetic excitation, will be responsible
for the color. The links can be of four types: covalent, ionic, metallic,
and of Van der Waals. |
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Sawing a large block of tourmaline in Madagascar, using a diamond blade.
The
metal disk must be continuously humidified by a jet of water in order to
lower its temperature. |
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Tourmalines
have a complex structure featuring various |
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polyhedral environments
for cations and which allow many |
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substitutions for
elements
as common as iron, titanium, |
Growth
zoning in a tourmaline from Alakamishy Itenina.
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manganese, magnesium, lithium,
chromium, etc.. under their |
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The tourmalines group
represents a privileged field of |
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investigation. By themselves,
the aforementioned metals, |
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commonplace in the earth's
crust, can account for all the |
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colors observed. |
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We
will keep this very telling example about the pink color |
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involved both a electronic colorful center and a color free |
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| center.
The work by K. Nassau on a large number of specimens |
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by irradiation and heating indicates the existence of at |
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seven different pinks. I.e. at the place where our eye can |
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see a pink shade, measuring devices detect seven distinct |
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| The
thickness of a ribboned polychrome |
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| tourmaline
cabochon usually reaches 3.5 to |
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| 5.5
mm. depending on the size of the stone. |
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| Wavelength: |
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Physics
knows wavelength of radiation only, the notion of color is
completely |
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foreign
to it. That's why it is so helpful to us in the interpretation of color
in |
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minerals.
A spectrograph that only identifies the position of spectral lines
will |
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perfectly
make the difference between a radiation at 0.530 microns and an
another |
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at
0.532 microns, where our eyes will only receive the same green. |
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