Brown diamonds
Encyclopedia
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
impurities and lattice defects associated with plastic deformation, the latter are considered as the predominant cause, especially in pure diamonds. A high-pressure high-temperature treatment has been designed to heal lattice defects and convert brown diamonds into yellow or even colorless stones.
Occurrence
Diamonds occur in various colors including yellow, green, orange, various shades of pink and red, brown, gray and black. Before the development of Argyle diamond mineArgyle diamond mine
The Argyle Diamond Mine is a diamond mine located in the East Kimberley region in the remote north of Western Australia. Argyle is the largest diamond producer in the world by volume, although due to the low proportion of gem-quality diamonds, is not the leader by value. It is the only known...
in Australia in 1986, most brown diamonds were considered worthless for jewelry; they were even not assessed on the diamond color
Diamond color
A chemically pure and structurally perfect diamond is perfectly transparent with no hue, or color. However, in reality almost no gem-sized natural diamonds are absolutely perfect. The color of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice...
scale, and were predominantly used for industrial purposes. However, the
marketing strategy changed in the 1980s and the brown diamonds are becoming popular gems. The change was mostly due to the numbers: the Argyle mine, with its 35 million carats (7,000 kg) of diamonds per year, makes about one third of global production of natural diamonds; 80% of Argyle diamonds are brown. The percentage of brown diamonds is lower in other mines, but it is almost always a significant part of the total production. Consequently, scientific research has intensified on causes of brown color in diamond and ways to alter it, as described below in the section causes of color.
Notable brown diamonds
- Golden Jubilee Diamond is currently the largest cut diamond in the world. It was found in 1985 as a rough stone of 755.5 carats (151 g) in the Premier minePremier MineThe Premier Mine is an underground diamond mine owned by Petra Diamonds. It is situated in the town of Cullinan, 40 kilometres east of Pretoria, Gauteng Province, South Africa. Established in 1902, it was renamed the Cullinan Diamond Mine in November 2003 in celebration of its centenary...
, South AfricaSouth AfricaThe Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
- one of the most famous diamond mines in the world operated by De BeersDe BeersDe Beers is a family of companies that dominate the diamond, diamond mining, diamond trading and industrial diamond manufacturing sectors. De Beers is active in every category of industrial diamond mining: open-pit, underground, large-scale alluvial, coastal and deep sea...
. The stone was cut into a 545.67-carat (109.13 g) and was purchased from De BeersDe BeersDe Beers is a family of companies that dominate the diamond, diamond mining, diamond trading and industrial diamond manufacturing sectors. De Beers is active in every category of industrial diamond mining: open-pit, underground, large-scale alluvial, coastal and deep sea...
by a group of businessmen led by Henry Ho of Thailand in 1995. The Golden Jubilee Diamond was named by King Bhumibol Adulyadej and given to him on occasion of his 50th coronation anniversary.
Earth Star Diamond was found at another South African mine of De Beers
De Beers
De Beers is a family of companies that dominate the diamond, diamond mining, diamond trading and industrial diamond manufacturing sectors. De Beers is active in every category of industrial diamond mining: open-pit, underground, large-scale alluvial, coastal and deep sea...
, the Jagersfontein Mine
Jagersfontein Mine
Jagersfontein Mine is an abandoned open-pit mine in South Africa located close to the town of Jagersfontein and approximately south-west of Bloemfontein. Since it was first established in 1888, two of the ten biggest diamonds ever discovered, the Excelsior and the Reitz , were mined from...
on May 16, 1967. The diamond came from the 2,500-foot (760 m) level of the volcanic diamond-bearing pipe. The rough gem weighed 248.9 carats (49.8 g) and was cut into a 111.59 carats (22.3 g) pear-shaped gem with a strong brown color and extraordinary brilliance. The diamond was bought in 1983 for $900,000.
- Star of the SouthStar of the SouthThe Star of the South, also known as Estrela do Sul, is a diamond found in Brazil in 1853. The diamond is cut into a cushion shape and weighs . The Star of the South is graded as a type IIa diamond, with a colour grading of fancy light pinkish-brown and a clarity of VS2. At the time of discovery,...
(original name was Portuguese "Estrela do Sul") is one of the largest diamonds found in Brazil and the first Brazilian diamond to receive international acclaim. The original rough stone was found in 1853 by an African slave woman, for which she received her freedom and life pension. The diamond was cut into a cushion shapeDiamond cutA diamond cut is a style or design guide used when shaping a diamond for polishing such as the brilliant cut. Cut does not refer to shape , but the symmetry, proportioning and polish of a diamond...
d gem weighing 128.48 carats (25.7 g). For a long time, the Star of the South was considered as "by far the largest diamond discovered by any woman anywhere", until the Incomparable Diamond was discovered in the 1980s. The diamond has a color grade of Fancy Light Pinkish-Brown.
- Incomparable Diamond is another African diamond, one of the largest ever found in the world (890 carats (178 g)). A young girl encountered it in 1984 a pile of rubble collected from old mine dumps of the nearby MIBA Diamond MineSocieté minière de BakwangaSocieté minière de Bakwanga is a mining company based in the Democratic Republic of the Congo. MIBA is a diamond mining company, and its operations are centered near Mbuji Mayi, in Kasai-Oriental Province in south central DRC....
, Democratic Republic of the CongoDemocratic Republic of the CongoThe Democratic Republic of the Congo is a state located in Central Africa. It is the second largest country in Africa by area and the eleventh largest in the world...
. The rubble was sorted out during the recovery process because it was considered too bulky to contain diamonds. This massive diamond was considered to be cut into the world's largest gem, but finally, the size was reduced to 407.5 carats (81.5 g) for the sake of having fewer internal flaws; nevertheless, it was the 3rd largest cut diamond after the Cullinan ICullinan DiamondThe Cullinan diamond is the largest rough gem-quality diamond ever found, at .The largest polished gem from the stone is named Cullinan I or the Great Star of Africa, and at was the largest polished diamond in the world until the 1985 discovery of the Golden Jubilee Diamond, , also from the...
and Golden Jubilee Diamonds. Before cutting, the stone was the largest brown diamond and the fourth largest diamond of any color ever discovered after the Cullinan (3106.75 carats (621.4 g)), Excelsior DiamondExcelsior DiamondThe Excelsior Diamond was found on June 30, 1893 at the Jagersfontein Mine by a worker while loading a truck. The man was able to hide the diamond from the supervisors but delivered it to the manager of the mine himself. Until 1905, when the larger Cullinan diamond was found, the Excelsior was the...
(995 carats (199 g)) and Star of Sierra LeoneStar of Sierra LeoneThe Star of Sierra Leone diamond was discovered by miners on February 14, 1972 in the Diminco alluvial mines in the Koidu area of Sierra Leone. It ranks as the third-largest gem-quality diamond and the largest alluvial diamond ever discovered....
(968.9 carats (193.8 g)). The stone was cut by a team led by Marvin Samuels, who co-owned the stone along with Donald Zale of Zales Jewellers and Louis Glick. In November 1984 the finished stones were put on display: a single golden diamond of 407.48 carats (81.5 g) in a 'trioletteDiamond cutA diamond cut is a style or design guide used when shaping a diamond for polishing such as the brilliant cut. Cut does not refer to shape , but the symmetry, proportioning and polish of a diamond...
' shape, and fourteen additional gems. Notably, the satellite stones cut from the Incomparable varied greatly in color, from near-colorless to rich yellow-brown. The largest of these stones still bears the name 'Incomparable Diamond', and was graded by the GIAGemological Institute of AmericaThe Gemological Institute of America, or GIA, is a nonprofit institute dedicated to research and education in the field of gemology and the jewelry arts. Founded in 1931, GIA's mission is to protect all buyers and sellers of gemstones by setting and maintaining the standards used to evaluate...
as internally flawlessDiamond clarityDiamond clarity is a quality of diamonds relating to the existence and visual appearance of internal characteristics of a diamond called inclusions, and surface defects called blemishes. Clarity is one of the four Cs of diamond grading, the others being carat, color, and cut...
in 1988.
- Lesotho Brown was unearthed at the Letseng diamond mineLetseng diamond mineThe Letseng diamond mine, found in the landlocked Southern African kingdom of Lesotho, is owned by Gem Diamonds, Ltd. and the government of Lesotho, and at an elevation of 3,100 m it is the world's highest diamond mine.- Production :...
in LesothoLesothoLesotho , officially the Kingdom of Lesotho, is a landlocked country and enclave, surrounded by the Republic of South Africa. It is just over in size with a population of approximately 2,067,000. Its capital and largest city is Maseru. Lesotho is a member of the Commonwealth of Nations. The name...
in 1967 at Letseng-la-Terai by Ernestine Ramaboa. The rough stone weighed 601 carats (120.2 g) and was cut in 1968 into 18 polished diamonds totaling 252.4 carats (50.5 g). The largest was a 71.73 carats (14.3 g) emerald cut known as the Lesotho I. The Lesotho III (the third largest stone cut from the crystal) is a 40.42 carats (8.1 g) marquise-shaped gem that was once owned by Jackie Kennedy, given to her by her husband Aristotle OnassisAristotle OnassisAristotle Sokratis Onassis , commonly called Ari or Aristo Onassis, was a prominent Greek shipping magnate.- Early life :Onassis was born in Karatass, a suburb of Smyrna to Socrates and Penelope Onassis...
. The ring had an estimated value of $600,000 US, but at the Jackie Kennedy estate sale auction in April 1996 it reached a price of $2,587,500 US dollars. It was mounted in a platinum ring created by Harry WinstonHarry WinstonHarry Winston was an American jeweler. He donated the Hope Diamond to the Smithsonian Institution in 1958 after owning it for a decade, and traded the Portuguese Diamond to the Smithsonian in 1963.-History:...
. The Lesotho I was offered at Sotheby'sSotheby'sSotheby's is the world's fourth oldest auction house in continuous operation.-History:The oldest auction house in operation is the Stockholms Auktionsverk founded in 1674, the second oldest is Göteborgs Auktionsverk founded in 1681 and third oldest being founded in 1731, all Swedish...
, Geneva on November 19, 2008 as part of a Magnificent Jewels sale, but it did not sell. It'd had a presale estimate of 3,360,000 to 5,600,000 Swiss francs, which equated to $2,783,894 to $4,639,824 US dollars. The lot's description mentioned it was being offered for sale by the same owner who had originally bought it from Harry Winston around 1969. It also listed the gem as having a clarity of VVS2, excellent polish and excellent symmetry, and although the stone (and the other Lesotho fragments) is a pale brown color, no color grade is mentioned in the auction text.
Irradiation
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s, ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s, neutron
Neutron
The neutron is a subatomic hadron particle which has the symbol or , no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of...
s or gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s) knocks off carbon atoms and produces vacancies
Crystallographic defect
Crystalline solids exhibit a periodic crystal structure. The positions of atoms or molecules occur on repeating fixed distances, determined by the unit cell parameters. However, the arrangement of atom or molecules in most crystalline materials is not perfect...
in the diamond lattice. Those vacancies produce green color centers
F-Center
An F-Center or Farbe center is a type of crystallographic defect in which an anionic vacancy in a crystal is filled by one or more electrons, depending on the charge of the missing ion in the crystal. Electrons in such a vacancy tend to absorb light in the visible spectrum such that a material...
in pure transparent diamond and yellow-green color in yellow diamonds. Yellow diamonds have color mostly due to nitrogen impurity and they constitute the majority of all natural diamonds. Heating the irradiated diamonds to temperatures above 600 °C results in brown color associated with aggregation of the vacancies, with or without nitrogen involved.
Such irradiation and annealing treatment can occur in nature because diamonds are often accompanied by uranium-containing ores which emit alpha particles. However, the thus produced color is restricted to a thin surface layer of few micrometers. Homogeneous color can be produced if the treatment is performed artificially, using electrons, neutrons or gamma-rays. Radiation treatment induces characteristic sharp optical absorption lines which can be easily detected by spectroscopic techniques.
Brown synthetic diamonds
Synthetic diamonds created by compressing graphite to several gigapascals and heating to temperatures above 1500 °C are usually rich in nitrogen. Nitrogen in those diamonds is dispersed through the lattice as single atoms and induces yellow color. Nickel is often added to graphite to accelerate its conversion into diamond. Incorporation of nickel and nitrogen into diamond induces brown color. Nickel is easily detectable by characteristic, sharp optical absorption and luminescence signals making such diamonds easily identifiable.Natural brown diamonds
Whereas the brown color due to irradiation or nickel impurity can be easily recognized through spectroscopic (e.g. absorption) measurements, the majority of natural brown diamonds do not show any characteristic absorption peaks. Whereas the consensus has been reached that the color relates to the plastic deformation, the particular reason has not been reliably identified yet. Extended lattice defectsCrystallographic defect
Crystalline solids exhibit a periodic crystal structure. The positions of atoms or molecules occur on repeating fixed distances, determined by the unit cell parameters. However, the arrangement of atom or molecules in most crystalline materials is not perfect...
such as dislocations and slip planes were the most popular candidate, however, recent results favor large clusters of vacancies (mini-voids) as a more likely cause. Those lattice defects are most likely responsible for the color of the notable diamonds described above.
Heat-treated brown diamonds
The observation that brown color might related to the lattice imperfections has led to a technique to convert brown diamonds into more valued light-yellow or even colorless ones: the diamond is subjected to high pressures of 6-10 GPa and temperatures above 1600 °C that heals (anneals) those defects. The technique has been demonstrated in several research laboratories in Russia and US. In March 1999, Pegasus Overseas Ltd (POL) from Antwerp, BelgiumBelgium
Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...
, a subsidiary of Lazare Kaplan International
Lazare Kaplan International
Lazare Kaplan International Inc. is a diamond manufacturing and distribution company based in New York City. The Chairman of the Board of Directors is Maurice Tempelsman.- Business activities :...
, has started marketing of such diamonds which were processed by the General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
(GE). Those diamonds have therefore received a name GE POL (or GEPOL) and were marketed in the US as Bellataire diamonds. The fact and the identity of the treatment process was considered so important that micrometer-sized letters "GEPOL" were inscribed with a laser on the girdles
Brilliant (diamond cut)
A brilliant is a diamond or other gemstone, cut in a particular form with numerous facets so as to have exceptional brilliance. The shape resembles that of a cone and provides maximized light return through the top of the diamond....
of every treated diamond. In 2004, however, the GE diamond section has been purchased by Littlejohn & Co.
Littlejohn & Co.
Littlejohn & Co. is a private equity firm focused on leveraged buyout transactions, leveraged recapitalizations of middle-market companies and distressed securities. The firm focuses on companies requiring an operational turnaround particularly in a variety of industrial and service sectors.The...
and renamed into Diamond innovations. Since 1999, several companies around the world have adopted the technique and use various brand names for the processed diamonds.