Great Chrysanthemum Diamond
Origin of name
The Great Chrysanthemum diamond gets its name from the Chrysanthemum flowers, as the rich golden brown color of the diamond, seems to have a close resemblance to the color of these beautiful brown flowers.
Characteristics of the diamond
The G. I. A. certificate of the diamond describes it as a pear-shaped, modified brilliant-cut, with a color grading of fancy brown and weighing 104.16 carats. The dimensions of the stone are 39.10 x 24.98 x 16.00 mm, and the stone has 67 facets on the crown, 57 facets on the pavilion, and 65 vertical facets along the girdle, making a total of 189 facets.
The Great Chrysanthemum is perhaps the 5th largest faceted brown diamond and the 2nd largest pear-shaped brown diamond in the world. See table below. The Golden Jubilee diamond, which is at the top of the table, is not only the largest faceted brown diamond, but also the largest of all faceted diamonds in the world.
List of famous brown diamonds
S/N
Name Carat Weight Shape/Cut color
1 Golden Jubilee 545.67 cushion fancy yellow brown 2 Star of the South 128.48 cushion fancy light pinkish brown 3 Earth Star 111.59 pear brown 4 Cross of Asia 109.26 radiant light brown 5 Great Chrysanthemum 104.16 pear fancy brown 6 Victoria Transvaal 67.89 pear champagne-light brown 7 Golden Maharajah 65.57 pear fancy dark orange brown 8 Kimberley 55.09 emerald light brown
History
The Great Chrysanthemum is a brown diamond discovered in one of the diamond mines in South Africa, in the year 1963. However the mine of origin of the diamond is not known. In the rough state the diamond weighed 198.28 carats and had a light honey color.
The rough stone was purchased by a jeweler from New York, Julius Cohen, in the same year it was discovered, and taken to New York. The task of cutting the stone was assigned to the diamond cutting firm Messrs. S & M Kaufmann of New York, who under the direction of Mr. Cohen himself, eventually fashioned the stone into a beautiful, rich golden-brown, pear-shaped faceted diamond, weighing 104.16 carats. The diamond was then mounted as the centerpiece of a necklace, consisting of marquise, pear, and round-shaped diamonds.
The Great Chrysanthemum diamond has been exhibited throughout the United States, at several diamond exhibitions. In the year 1965, the Great Chrysanthemum, was named as a winner of one of the Diamonds International Awards. Again in the same year, the diamond was exhibited, in the Diamonds International Academy Collection, at the Diamonds Pavilion in Johannesburg, South Africa. In 1971, the diamond was exhibited at the Kimberley Centenary Exhibition held in South Africa.
Julius Cohen later sold the diamond to an anonymous, reputed, foreign buyer, but presently the owners of the diamond are Garrards of London.
Chemistry of brown diamonds
Color in diamonds can be due to three possible reasons :
1 - Presence of impurities in the crystal structure. Diamonds are crystalline allotropic form of Carbon. Certain elements like nitrogen, boron, or hydrogen that have atomic sizes comparable to that of Carbon, can be incorporated in the crystal structure of diamond, replacing some of the carbon atoms. The presence of these impurities can impart color to the diamonds by absorbing light in different regions of the visible spectrum, that brings out complementary colors to the color that is absorbed. eg. Nitrogen can absorb light in the blue end of the spectrum, bringing out the yellow color that is complementary to blue. Likewise nitrogen can sometimes absorb light in the green region of the spectrum, imparting the complementary color orange. Boron imparts a blue color to the diamonds. Hydrogen imparts grey, violet and sometimes green color to diamonds.
2 - Plastic deformation of the crystal structure. The tetrahedral crystal units of diamond can sometimes undergo twisting and bending during it's formation or subsequent rise to the surface from deep inside the earth's crust, a process that took perhaps 2 to 3 billion years or more. Such deformed areas in the crystal can alter the absorption spectrum of the stone, imparting pink, purple, red and brown colors to diamonds.
3 - Exposure to natural irradiation. Exposure to long periods of irradiation lasting millions of years, causes "radiation burns", in the form of small patches, usually only skin deep. These patches are actually areas where the atomic structure has been altered, which changes the absorption spectrum, imparting a green color to the diamonds.
The Presence of impurities and deformation of crystal structure (1 and 2 above) can sometimes occur together giving a combination of colors eg. Nitrogen impurities together with plastic deformation can cause color combinations such yellowish brown, brownish yellow, orangish brown and brownish orange.
Thus brown color in diamonds can be caused by plastic deformation alone, in which case they are Type IIa diamonds or they can be caused by plastic deformation in combination with presence of nitrogen, in which case they are Type 1a or rarely Type 1b diamonds. It is sometimes stated that brown color in diamonds is caused by stress zones in the crystal. This is same thing as saying plastic deformation, because it is the bending and twisting of the crystal units that creates the stress zones in the giant molecule.
Diamond Classification
Diamonds are classified into two main types depending on the presence or absence of nitrogen :- Type 1 and Type 11
Type 1 - Contain detectable quantities of nitrogen. 98 % of all naturally occurring diamonds belong to this group.
Type 11- Nitrogen free or contain undetectable quantities of nitrogen. Only 1-2 % of naturally occurring diamonds belong to this group.
Type 1 - Type I diamonds are sub-divided into two :- Type 1a and Type 1b
Type 1a - Nitrogen atoms distributed as groups of two or more atoms. Groups of two atoms are called A-aggregates, and groups of four atoms are called B-aggregates. Groups of three atoms are called N3 centers. Almost 98 % of naturally occurring diamonds are Type 1a. These diamonds can be colorless or more frequently pale to medium yellow in color, and rarely orange.
Type 1b - Nitrogen atoms are scattered as single atoms in the crystal structure. Only 0.1 % of naturally occurring diamonds belong to this group. The diamonds have an intense yellow or orange colors. Canary yellow diamonds belong to this group.
Type II diamonds are sub-divided into two :- Type IIa and Type IIb
Type IIa - Free of all impurities, and usually have perfectly formed crystals. Thus factors that can cause colors are absent. Therefore these diamonds are absolutely colorless and are known as the "purest of the pure" of all diamonds. 1-2 % of all natural diamonds belong to this group. However some Type IIa diamonds have undergone plastic deformation, producing colors such as red, purple, pink, brown etc. Their occurrence is less than 0.1 % of all natural diamonds.
Type IIb - Free of nitrogen impurities but instead contain trace quantities of boron, which impart a blue color to the diamonds. Their occurrence is however less than 0.1 % of all natural diamonds.
Argyle brown diamonds
Argyle diamond mines in Western Australia has an average annual production of around 35 million carats, which represents about a third of the global production of natural diamonds. Almost 50 % of this annual production is industrial diamonds, followed by 45 % of near-gem quality diamonds. Only 5% of the total production is gem-quality.
Out of the 5 % of gem-quality diamonds produced, 80% are brown, 16 % yellow, 2 % white, 2 % grey, and less than 1 % fancy colored diamonds, such as pink, red, and green. Despite the low output of pink and red diamonds, the Argyle diamond mines is the only consistent source of these diamonds in the world today.
Most of the Argyle diamonds, whether brown, yellow or pink are Type Ia diamonds having varying quantities of nitrogen. The nitrogen content of colorless diamonds are 500 to 1,000 ppm, brown diamonds, 100 to 500 ppm and the pink diamonds, 10 to 100 ppm. In the case of brown diamonds while the nitrogen imparts a yellow or orange color, the structural defects impart a brown color, giving a range of colors such as brownish yellow, yellowish brown, orangish brown and brownish orange, and dark brown colors.
Argyle Diamond Mining Company has introduced a color grading scale for their brown diamonds.
Argyle's color grading for brown diamonds
Color
Argyle Term Argyle Color Grade
Very light brown light champagne C1 - C2 Medium brown medium champagne C3- C4 Brown dark champagne C5-C6 Dark brown fancy cognac C7
Most of the diamonds produced in the Argyle mines are small, and the processing of these diamonds is very labor intensive and required skilled manpower. The Companies controlling the Argyle mines have established a partnership with leading diamond cutting firms in India, to process their large output of small brown diamonds. This partnership is mutually advantageous to both sides. While the Indian firms were getting sufficient quantities of rough diamonds to feed their booming diamond processing industry, the Argyle diamond mining companies, were getting their diamonds processed at affordable costs, making their industry economically viable and sustainable. The companies are marketing their products as cognac and champagne diamonds, and jewelry set with these diamonds have become increasingly popular, ensuring the economic viability of these mines.
You are welcome to discuss this post/related topics with Dr Shihaan and other experts from around the world in our FORUMS (forums.internetstones.com)
