Characteristics of the
diamond
The diamond is a round brilliant-cut, deep purple, stone
weighing 2 to 5 carats. The exact weight of the stone, color and clarity
grades have not been revealed, but by all accounts this rare diamond
appears to be unique for more than one reason. While at one angle the
diamond appears to have a deep purple color, the color changes to a crimson
when it is slowly rotated in the light. Some authorities have characterized
this diamond as a color- change diamond, the first of it's kind discovered
in the world. But, the validity of such a characterization is questionable,
as in other color-change gemstones like Alexandrites, the term is
applied to color changes occurring in two different sources of light, normal
daylight and artificial light.
The diamond therefore appears to have a combination of
two of the rarest colors in fancy colored diamonds, viz. purple and crimson
(deep red). The colors are quite deep and vivid. The "Supreme Purple Star"
diamond can therefore be characterized as the "rarest of the rare" colored
diamonds in the world.
Early history
Being a relatively new discovery, the diamond does not
have much of a history associated with it, but it is hoped that this rare
and unique stone will build up it's own myths and legends as it passes down
the lane of posterity.
However, the early history of the diamond such as the
country of origin, the mine of origin, the date of discovery, the weight and
characteristics of the rough stone, the original owner of the diamond, the
country where the diamond was processed etc. are all unknown, but, the
diamond is believed to have originated in the Amazon basin at least 25 years
ago.
The weight of the diamond, 2 to 5 carats, is in keeping
with the smaller size of such rare diamonds. Eg:- The world's 1st, 2nd, and
3rd largest red diamonds, the "Moussaieff red," the "red diamond," and
the "De Young Red," weigh only 5.11, 5.05 and 5.03 carats respectively.
According to British press reports , the rare diamond
surfaced in London, in the year 2002. Until then the anonymous owner of the
diamond perhaps, was not aware that the gem was a diamond and that too a
very rare category of diamond indeed ! Only when he decided to take the stone
for valuation, was it revealed that the stone was an extremely rare specimen
of a fancy purple diamond.
It is difficult to believe that such a rare diamond
could have remained undiscovered for the last 25 years, after it was cut and
polished into a finished gem. Any experienced cutter would have identified
the stone as as a diamond, while in the process of cutting , given the
hardness of the diamond, and the special difficulties that have to be
surmounted in the cutting and polishing of a diamond. Even if the stone had
been identified and processed as a diamond, any experienced cutter would
have known the rarity and the valuation of such a rare stone. The fact that
the stone has been cut as a round brilliant, the commonest cut employed for
diamonds indicates that the cutter had prior knowledge that the gem was a
diamond.
Be that as it may, it is reported that the owner of the
stone wants to get it graded by a renowned laboratory, with a view of
disposing of it in the near future.
Pricing of colored
diamonds
With respect to the pricing of colored diamonds, besides
the common criteria of cut, clarity, shape, and weight used in the pricing
of colorless or white stones, additional criteria of the rarity of the color
and it's intensity also play a very important part in the pricing of colored
diamonds. Thus the prices of exceptional quality, rare colored, diamonds are
generally much higher than the corresponding colorless or white diamonds.
In the case of the "Supreme Purple Star" diamond the
rarity of the color, combined with the color changing property and the deep
and vivid colors could make it one of the most expensive diamonds on a
per carat basis.
the 0.95-carat "Hancock Red" diamond set a world record
in terms of pricing in 1987 and was sold for U.S. $ 880,000, which works out
to U.S. $ 926,315 per carat. The 'Supreme Purple Star" has the potential, to
break this 20-year old world record, and earn the rare distinction of being
the world's most expensive diamond on a per-carat basis. The owners of the
diamond are hoping that it will fetch about $ 4 million per carat.
Chemistry of fancy
colored diamonds
Pink, red, purple, blue, green, yellow,
orange etc. are known as fancy colors in the gem and diamond trade.
Yellow and brown are the commonest colors in diamonds.
Blue, green, and pink are rare, but the rarest colors are red and purple.
Color in diamonds are caused in three possible ways :-
(1) Incorporation of impurities in the
crystal structure.
(2) Plastic deformation of the crystal
structure.
(3) Exposure to irradiation
(1) Incorporation of impurities in the crystal
structure:-
Diamond is a crystalline form of Carbon. If the diamond
crystal is pure and perfect consisting of carbon atoms only without any
impurities, the diamond is absolutely colorless. Only 1-2 % of all natural
diamonds are of this exceptional quality. The common impurity in diamonds is
Nitrogen (less than 0.1 %) which imparts a yellow color to diamonds, if scattered in the crystal as single atoms or groups of 3-atoms (N3 centers).
The yellow color can vary from a slight tinge to an intense yellow (canary).
If Nitrogen atoms are scattered as groups of 2-atoms or 4-atoms the diamond
remains colorless. 98 % of all naturally occurring diamonds contain Nitrogen
atoms as aggregates. Only 0.1 % of diamonds contain Nitrogen atoms scattered
as single atoms.
Some diamonds contain Boron as impurity instead of
Nitrogen. However they are only 0.1 % of all naturally occurring diamonds.
Boron imparts a blue color to diamonds. This explains the rarity of
blue diamonds.
(2) Plastic deformation of the crystal structure:-
A perfectly formed crystal of diamond is an absolutely
colorless crystal. But, such naturally formed perfect crystals are very
rare. Diamonds are up to 3 or 4 billion years old. The crystallization of
diamonds took place around 200 Kilometers below the surface of the earth, in
it's mantle, and were later transported to the surface via Kimberlite and
Lamproite pipes, which acted as conduits, from the earth's mantle to the
continental crust. In the process of it's gradual movement towards the
surface, which perhaps took millions of years, the diamond crystals were
subjected to very high temperatures and pressures and the tetrahedral
crystal units of some of the crystals underwent twisting and bending and
were put under enormous strain. This is known as plastic deformation. Such
deformed areas in the crystal can absorb light in different areas of the
visible spectrum imparting different colors such as pink. red, purple,
orange ,brown etc, and such colors are shown only if it happened in
the rare 1-2 % of the Nitrogen free absolutely colorless diamonds. Hence the
rarity of fancy colored diamonds. However in the Argyle mines in western
Australia, which produce large quantities of brown diamonds most of them
appear to be plastically deformed.
(3) Exposure to irradiation :-
When the diamond crystal with or without Nitrogen
impurities was exposed to prolonged natural irradiation for millions of
years both during the formation of the crystal and after, it absorbed
magenta wavelengths that imparted a green color to the diamond. Such
naturally irradiated green diamonds are extremely rare, eg. the
Dresden Green diamond.
