Red diamonds are usually
structurally imperfect Type IIa diamonds, in which the red color is caused
by plastic distortion of the crystal structure of the diamond either
during its formation in the earth's mantle or subsequent rise to the
earth's surface during volcanic eruptions. Type II diamonds are free of
nitrogen or contain undetectable quantities of nitrogen. However, most of
the diamonds produced in the Argyle diamond mines, including the pink and
red diamonds contain detectable quantities of nitrogen, which are found as
aggregates and are therefore Type Ia diamonds. The nitrogen content of
pink and red diamonds is 10 - 100 ppm (parts per million), and they are
found as A and B aggregates, which do not affect the color of the
diamonds. However, plastic distortion in the crystal structure produces
the pink and red colors. Therefore pink and red diamonds produced in the
Aryle diamond mines are classified as Type Ia diamonds.
History
The diamond was one of 65 pink colored diamonds recovered
from the Argyle diamond mines production for the year 2006. The diamonds
intense purplish-red color separated it from the other 64 diamonds which
were intense pink in color. The rough diamond weighed 1.46 carats, and was
probably cut and polished by the highly trained craftsmen at the
state-of-the-art diamond processing center at Perth, the capital of Western
Australia, using advanced technology in the form of laser devices, automatic
bruting, and computerized polishing equipment. After cutting and polishing
the round brilliant-cut diamond had a weight of only 0.54 carats and a
diameter of 5.13 mm.
The "Lady in Red" diamond came up for
auction at the Argyle mines pink diamond tender for the year 2006 and was
one of 65 diamonds that appeared at the auction. The diamond was purchased
by a Brisbane jeweler Cameron Robinson, managing director of Bruce Robinson
diamonds, but the purchase price of the diamond has not been revealed.
According to Mr. Robinson the diamond is only one of seven such red diamonds
ever found in the world. This seems to agree with our list of known red
diamonds given above, but according to other sources there are around 20
diamonds in the world including the seven above that are certified as red.
In any case the occurrence of red diamonds is extremely
rare. Mr. Robinson says that the chances of finding a red diamond is one in
60 million. This figure is correct as seen in the following computation.
According to a statistical estimate, at the Argyle diamond mines, only a
single carat of pink diamond is produced for every one million carats of
rough diamonds. Thus the probability of occurrence of pink diamonds is
1/1,000,000 or one in one million. Out of an average of 60 pink
diamonds produced annually at the mines only an average of one diamond is
red. Thus the probability of occurrence of a red diamond out of the total
pink diamond production is 1/60. Therefore the probability of occurrence of
a red diamond out of the total annual production at the Argyle mines is
1/1,000,000 x 1/60, which works out to 1/60,000,000 or one in 60 million.
Argyle diamond production
The Argyle diamond mines are situated in the remote
north-east region of Western Australia, over 2,000 Km from Perth, the state
capital. The diamond pipe in Argyle is not the usual Kimberlite pipe, but a
Lamproite diamond pipe. The Argyle mine is the world's largest producer of
diamonds by volume, but due to low proportion of gem-quality diamonds, in
terms of value, Argyle is not the leading producer. The average annual
production of diamonds is around 35 million carats (7,000 Kg), which is
almost one-third of the world's annual production of natural diamonds. Out
of this enormous production only 5 % is considered to be gem-quality, and of
the remainder 55 % is industrial quality, and 40 % near gem-quality. In
comparison, the percentage of gem-quality diamonds in the rough production
of diamonds from mines around the world is about 20 %. Out of the 5 %
gem-quality diamonds produced almost 80 % are brown, 16 % brownish yellow
and yellow, 2 % white, 2 % grey and less than 1 % pink, red and green. Even
in terms of size Argyle diamonds are quite small. Most of the diamonds
produced are less than 1.0 carat in size. The largest diamond crystal
discovered so far weighs only 42.6 carats, and was found in 1991.
Processing of Argyle diamonds
The Argyle mine has ore processing and diamond sorting
facilities on site. The company has introduced a state-of-the-art X-ray
diamond sorting technique that could sort approximately 200 diamonds per
second at peak sorting rates. The sorted rough diamonds are washed and
shipped to Perth for further sorting. At first the diamonds are sorted
mechanically according to size through a series of mechanical sieves. After
sieving, the rough stones are sorted according to shape and color using
sophisticated equipment. After the mechanical sorting is completed the final
sorting is done by experienced human sorters who examine each stone
carefully and sort them based on size, shape, color and clarity. The best
quality gems that constitute less than 1 % of the production and appear
mainly as pink diamonds and an occasional red or green diamond, is retained
by Argyle, to be processed in their state-of-the-art processing center at
Perth. A substantial proportion of the annual diamond production, especially
the brown diamonds of smaller sizes are dispatched to the diamond cutting
centers of India for processing, and are eventually transformed into
champagne and cognac diamonds.
Marketing of Argyle diamonds
The Argyle mines in consultation with their Indian
partners adopted a strategy to popularize their enormous production of brown
diamonds. They produced jewelry of all types set with these brown diamonds,
and marketed them as champagne and cognac diamonds. Within a short time the
new range of brown diamond jewelry became very popular among consumers, and
the demand is increasing. The marketing strategy was successful, and the
economic viability of the Argyle mines had been ensured.
Diamond Tenders
To market the mines high quality colored stone
production, which was mainly pink, and constituted only about 1 % of the
total production, the company adopted an entirely different strategy. They
introduced a system of auctions known as "diamond tenders", that was held
for specially invited clients. Every diamond tender was preceded by the
distribution of a tender catalogue, and viewings were held at important
diamond trading centers around the world, such as New York, London, Geneva,
Hong Kong, Tokyo and Sydney. The average size of these polished pink
diamonds were about 1.0 carat in size, and annually about 50 to 60 of these
diamonds were sold. Occasionally a red or green diamond might also be
included in these lots, but this is very scarce. This is because of the
extreme rarity of these diamonds in nature. The "Lady in Red" diamond is one
such scarce diamond that appeared at a diamond tender in the year 2006.
Prices of over $ 100,000 have been achieved for the pink diamonds, and since
1985 more than 700 stones, with a total weight of 550 carats had been sold
at these tenders.
Special characteristics of Argyle diamonds
All Argyle diamonds whether brown, yellow, colorless,
grey, pink, red or green are Type Ia diamonds. This is because these
diamonds have significant quantities of nitrogen varying from about 10 ppm
to about 1000 ppm, in the form of A and B aggregates, which do not affect
the color of diamonds. A great majority of the Agyle diamonds have undergone
deformation of the crystal lattice, and the diamonds are highly strained and
color zoned, parallel to {111}. The highly strained character is apparent
when observed with cross polarizing filters. The plastic deformation causes
the brown and pink coloration and other fancy colors like purple and red.
The red color in the "Lady in Red diamond" is also caused by plastic
deformation. Argyle brownish yellow and yellow diamonds however, contain N3
centers besides A and B aggregates, that impart the yellow color to the
diamonds. Brownish yellow color is the combined effect of plastically
deformed centers and N3 centers.
