The Cullinan II Diamond.

Imperial State Crown: originally made for Queen Victoria's coronation in 1838, it was remade for George VI in 1937. It contains the 317.40 carat Cullinan II. The large stone above the Cullinan II is the Black Prince's Ruby, which is actually a red spinel. The stone was at one time a giant bead. Note the red dot on the upper part of the stone - that is a ruby that was used to plug a small hole that went right through the stone. The Stuart Sapphire is a very fine 104-carat oval shaped sapphire that appears on the backside of the crown. It was amoung the Crown Jewels of Charles II. The sapphire in the center of the cross on the top of the crown is St. Edward's Sapphire, (believed to have belonged to Edward the Confessor), and the four large drop-shaped pearls are said to have been Elizabeth I's earrings.

The Cullinan

he Black Prince's Ruby on the front of the Imperial State Crown, a name which is misleading because the stone is actually a red spinel weighing about 170 carats. The gem is a large bead - the lighter-colored dot on the front of the stone is actually a ruby plugging up the hole that goes through the stone. Photo © HMSO,

The Cullinan

Late one afternoon in 1905, Mr. Frederick Wells, the superintendent of the prolific Premier Mine in South Africa, was making a routine inspection trip through the mine when his attention was attracted by something reflecting the last slanting rays of the setting sun. Curious, he stopped for a closer look. He was eighteen feet below the surface of the earth, and the shiny object was on the steep wall of the mine a few feet above him. Mr. Wells quickly scaled the wall and extracted from the blueground what appeared to be a large diamond crystal. At first, he thought he was being fooled by a large piece of glass, but tests proved it to be the largest gem-quality diamond ever discovered. It weighed 3106 carats, or about 1⅓ pounds. It was named after Sir Thomas Cullinan, who opened the mine and was visiting on that eventful day. Many diamond experts believe that the huge stone was only a fragment, and that another piece, (possibly as large or even larger) either still exists and awaits discovery, or was crushed in the mining process. The latter is very unlikely. The prospect of finding the portion of the Cullinan has added zest to the activities of numerous miners and prospectors. The Cullinan was sold to the Transvaal government, which presented it to King Edward VII on his 66th birthday on November 9th, 1907. It was insured for $1,250,000 when it was sent to England. The King entrusted the cutting of the stone to the famous Asscher's Diamond Co. in Amsterdam, which had cut the Excelsior and other large gems. T

Cullinan Diamond

The Cullinan diamond is the largest rough gem-quality diamond ever found, at 3,106.75 carats (621.35 g).^[1]

The largest polished gem from the stone is named Cullinan I or the First Star of Africa, and at 530.2 carats (106.0 g) ^[2] was the largest polished diamond in the world until the 1985 discovery of the Golden Jubilee Diamond, 545.67 carats (109.13 g), also from the Premier Mine. Cullinan I is now mounted in the head of the Sceptre with the Cross. The second largest gem from the Cullinan stone, Cullinan II or the Lesser Star of Africa, at 317.4 carats (63.5 g), is the fourth largest polished diamond in the world. Both gems are in the Crown Jewels of the United Kingdom.

Koh-i-Noor

The Kōh-i Nūr (Hindi: कोहिनूर, Persian/Urdu: کوہ نور, Telugu: కోహినూరు) which means "Mountain of Light" from Persian, also spelled Kohinoor, Koh-e Noor or Koh-i-Nur is a 105 carat (21.6 g) diamond that was once the largest known diamond in the world. The Kohinoor originated at Golconda in the state of Andhra Pradesh in India. It has belonged to various Sikh, Mughal and Persian rulers who fought bitterly over it at various points in history and seized it as a spoil of war time and again. After completely ignoring Maharaja Ranjit Singh's will^[1] it was finally seized by the East India Company and became part of the British Crown Jewels when British Prime Minister Benjamin Disraeli proclaimed Queen Victoria Empress of India in 1877.

Dresden Green Diamond

The Dresden Green diamond is a 41 carats (8.2 g) natural green diamond that has a historical record dating to 1722, when a London news-sheet carried an article about it in its 25 October-27th edition.^[1]

It is named after the capital of Saxony, Germany where it has been on display for most of the last two centuries. In 2000, American jeweler, Harry Winston arranged to display the Dresden Green in their New York Grand Salon and then at the Smithsonian in Washington DC, USA , where it was displayed in the Harry Winston pavilion next to the largest blue diamond in the world, the Hope diamond.

The stone's unique green color is due to natural exposure to radioactive materials (see Diamond enhancement#Irradiation). The stone is being used to compare natural versus lab-produced green diamonds — it is hoped that it can be used to devise a test to differentiate between naturally green diamonds, which are quite rare, and lab-produced ones.^[2]

This diamond is located in the Staatliche Kunstsammlungen Dresden "The New Green Vault" ^[3]

Noor-ol-Ain Diamond

The Noor-ol-Ain is the principle diamond mounted in a tiara of the same name made for Iranian Empress Farah Pahlavi's wedding to Shah Mohammad Reza Pahlavi in 1958. The Diamond is believed to have been recovered from the Golconda mines in India and was brought into the Iranian Imperial collection after the conquest of that country by Nader Shah Afshar in the 18th century.

It is one of the largest pink diamonds in the world and is believed to have once formed part of an even larger gem. That larger diamond is thought to have been cut in two, with one section becoming the Noor-ol-Ain and the other the Darya-ye Noor diamond. Both of these pieces are currently part of the Iranian Crown Jewels.^[1]

Noor-ol-Ain translated from Persian (via Arabic loan) means the light of the eye.

Irradiation

Sir William Crookes, a gem connoisseur as well as a chemist and physicist, was the first to discover radiation's effects on diamond color when in 1904 he conducted a series of experiments using radium salts. Diamonds enveloped in radium salt slowly turned a dark green; this color was found to be localized in blotchy patches, and it did not penetrate past the surface of the stone. The emission of alpha particles by the radium was responsible. Unfortunately radium treatment also left the diamond strongly radioactive, to the point of being unwearable ^[2]. A diamond octahedron so treated was donated by Crookes to the British Museum in 1914, where it remains today: it has not lost its color nor its radioactivity.

Nowadays diamond is safely irradiated in four ways: proton and deuteron bombardment via cyclotrons; gamma ray bombardment via exposure to cobalt-60; neutron bombardment via the piles of nuclear reactors; and electron bombardment via Van de Graaff generators. These high-energy particles physically alter the diamond's crystal lattice, knocking carbon atoms out of place and producing color centers. Irradiated diamonds are all some shade of green, black, or blue after treatment, but most are annealed to further modify their color into bright shades of yellow, orange, brown, or pink. The annealing process increases the mobility of individual carbon atoms, allowing some of the lattice defects created during irradiation to be corrected. The final color is dependent on the diamond's composition and the temperature and length of annealing.

Cyclotroned diamonds have a green to blue-green color confined to the surface layer: they are later annealed to 800°C to produce a yellow or orange color. They remain radioactive for only a few hours after treatment, and due to the directional nature of the treatment and the cut of the stones, the color is imparted in discrete zones. If the stone was cyclotroned through the pavilion (back), a characteristic "umbrella" of darker color will be seen through the crown (top) of the stone. If the stone was cyclotroned through the crown, a dark ring is seen around the girdle (rim). Stones treated from the side will have one half colored deeper than the other. Cyclotron treatment is now uncommon.

Gamma ray treatment is also uncommon, because although it is the safest and cheapest irradiation method, successful treatment can take several months. The color produced is a blue to blue-green which penetrates the whole stone. Such diamonds are not annealed. The blue color can sometimes approach that of natural Type IIb diamonds, but the two are distinguished by the latter's semiconductive properties. As with most irradiated diamonds, most gamma ray-treated diamonds were originally tinted yellow; the blue is usually modified by this tint, resulting in a perceptible greenish cast.

Thermal and electrical

Diamond is an extremely effective thermal conductor and usually an electrical insulator. The former property is widely exploited in the use of an electronic thermal probe to separate diamonds from their imitations. These probes consist of a pair of battery-powered thermistors mounted in a fine copper tip. One thermistor functions as a heating device while the other measures the temperature of the copper tip: if the stone being tested is a diamond, it will conduct the tip's thermal energy rapidly enough to produce a measurable temperature drop. As most simulants are thermal insulators, the thermistor's heat will not be conducted. This test takes about 2–3 seconds. The only possible exception is moissanite, which has a thermal conductivity similar to diamond: older probes can be fooled by moissanite, but newer Thermal and Electrical Conductivity testers are sophisticated enough to differentiate the two materials. Latest development is nano diamond coating, a nano layer of diamond material. If not tested properly it may show the same characteristics as a diamond Diamond Testing.

A diamond's electrical conductance is only relevant to blue or gray-blue stones, because the interstitial boron responsible for their color also makes them semiconductors. Thus a suspected blue diamond can be affirmed if it completes an electric circuit successfully.

The ring Main article: Engagement ring

The origin of the custom to use diamonds in rings, and more recently, in engagement rings, can be traced back to the Middle Ages and even the Romans. The Romans valued the diamond entirely on account of the supernatural powers they ascribed to it. Pliny wrote that a diamond baffles poison, keeps off insanity, and dispels vain fears.^[18] The medieval Italians copied these beliefs and added some to it: they called it the "Pietra della Reconciliazone" because it maintained concord between husband and wife. On this account it was recommended as the stone to be set in wedding (or espousal) rings—not on account of its beauty therefore, which was described by Isidore of Seville as a small stone devoid of beauty.^[18]

In more recent times a Parisian Oracle of mystic subjects, the Baron d'Orchamps, announced the diamond, if worn on the left (hand) warded off evil influences and attracted good fortune and since he had fashionable clients the word spread and the wearing of the diamond on the left hand became in itself a fashion.^[21]

One of the first occurrences of the diamond engagement (or wedding) ring can be traced back to the marriage of Maximilian I (then Archduke of Austria) to Mary of Burgundy in 1477.^[22] Other early examples of betrothal jewels incorporating diamonds include the Bridal Crown of Blanche (ca. 1370–80)^[22] and the Heftlein brooch of Vienna (ca. 1430–40),^[22] a pictorial piece depicting a wedding couple.

The popularity of the diamond ring as an engagement ring for a much wider audience can be traced directly to the marketing campaigns of De Beers, starting in 1938.^[23] Such a campaign had become necessary to sell the large quantity of diamonds suddenly available because of the large diamond finds particularly in South Africa.

Process Main article: Diamond cutting

The process of shaping a rough diamond into a polished gemstone is both an art and a science. The choice of cut is often decided by the original shape of the rough stone, location of the inclusions and flaws to be eliminated, the preservation of the weight, popularity of certain shapes amongst consumers and many other considerations. The round brilliant cut is preferred when the crystal is an octahedron, as often two stones may be cut from one such crystal. Oddly shaped crystals such as macles are more likely to be cut in a fancy cut—that is, a cut other than the round brilliant—which the particular crystal shape lends itself to.

Even with modern techniques, the cutting and polishing of a diamond crystal always results in a dramatic loss of weight; rarely is it less than 50%. Sometimes the cutters compromise and accept lesser proportions and symmetry in order to avoid inclusions or to preserve the carat rating. Since the per carat price of diamond shifts around key milestones (such as 1.00 carat (200 mg)), many one-carat diamonds are the result of compromising "Cut" for "Carat." Some jewelry experts advise consumers to buy a 0.99 carats (200 mg) diamond for its better price or buy a 1.10 carats (220 mg) diamond for its better cut, avoiding a 1.00 carat (200 mg) diamond which is more likely to be a poorly cut stone

Cut Main article: Diamond cut

Diamond cutting is the art and science of creating a gem-quality diamond out of mined rough. The cut of a diamond describes the manner in which a diamond has been shaped and polished from its beginning form as a rough stone to its final gem proportions. The cut of a diamond describes the quality of workmanship and the angles to which a diamond is cut. Often diamond cut is confused with "shape".

There are mathematical guidelines for the angles and length ratios at which the diamond is supposed to be cut in order to reflect the maximum amount of light. Round brilliant diamonds, the most common, are guided by these specific guidelines, though fancy cut stones are not able to be as accurately guided by mathematical specifics.

The techniques for cutting diamonds have been developed over hundreds of years, with perhaps the greatest achievements made in 1919 by mathematician and gem enthusiast Marcel Tolkowsky. He developed the round brilliant cut by calculating the ideal shape to return and scatter light when a diamond is viewed from above. The modern round brilliant has 57 facets (polished faces), counting 33 on the crown (the top half), and 24 on the pavilion (the lower half). The girdle is the thin middle part. The function of the crown is to diffuse light into various colors and the pavilion's function to reflect light back through the top of the diamond.

Tolkowsky defined the ideal dimensions as:

• Table percentage (table diameter divided by overall diameter) = 53%
• Depth percentage (Overall depth divided by the overall diameter) = 59.3%
• Pavilion Angle (Angle between the girdle and the pavilion) = 40.75°
• Crown Angle (Angle between the girdle and the crown) = 34.5°
• Pavilion Depth (Depth of pavilion divided by overall diameter) = 43.1%
• Crown Depth (Depth of crown divided by crown diameter) = 16.2%

The culet is the tiny point or facet at the bottom of the diamond. This should be a negligible diameter, otherwise light leaks out of the bottom. Tolkowsky's ideal dimensions did not include a culet. However, a thin culet is required in reality in order to prevent the diamond from easily chipping in the setting. A normal culet should be about 1%–2% of the overall diameter.

The further the diamond's characteristics are from Tolkowsky's ideal, the less light will be reflected. However, there is a small range in which the diamond can be considered "ideal." Today, because of the relative importance of carat weight in society, many diamonds are often intentionally cut poorly to increase carat weight. There is a financial premium for a diamond that weighs the magical 1.0 carat (200 mg), so often the girdle is made thicker or the depth is increased. Neither of these tactics make the diamond appear any larger, and both greatly reduce the sparkle of the diamond. So a poorly cut 1.0 carat (200 mg) diamond may have the same diameter and appear as large as a 0.85 carats (170 mg) diamond. The depth percentage is the overall quickest indication of the quality of the cut of a round brilliant. "Ideal" round brilliant diamonds should not have a depth percentage greater than 62.5%. Another quick indication is the overall diameter. Typically a round brilliant 1.0 carat (200 mg) diamond should have a diameter of about 6.5 mm. Mathematically, the diameter in millimeters of a round brilliant should approximately equal 6.5 times the cube root of carat weight, or 11.1 times the cube root of gram weight, or 1.4 times the cube root of point weight.

Ideal cuts can be controversial as the definitions of brilliance and beauty are very subjective.

Tolkowsky's mathematical model is now superseded by the GIA Facetware software that is the culmination of 20 years of studies on diamond cuts.

New diamond cuts are now all the rage in the diamond industry as for example a design invented in 2003 and called the Genesis cut. This cut differs in shape from the more traditional cuts in its concave surfaces and angles and resembles a 4-pointed star.

Color

Most diamonds used as gemstones are basically transparent with little tint, or white diamonds. The most common impurity, nitrogen, replaces a small proportion of carbon atoms in a diamond's structure and causes a yellowish to brownish tint. This effect is present in almost all white diamonds; in only the rarest diamonds is the coloration from this effect undetectable. The GIA has developed a rating system for color in white diamonds, from "D" to "Z" (with D being "colorless" and Z having a bright yellow coloration)[1], which has been widely adopted in the industry and is universally recognized, superseding several older systems once used in different countries. The GIA system uses a benchmark set of natural diamonds of known color grade, along with standardized and carefully controlled lighting conditions. Diamonds with higher color grades are rarer, in higher demand, and therefore more expensive, than lower color grades. Oddly enough, diamonds graded Z are also rare, and the bright yellow color is also highly valued. Diamonds graded D-F are considered "colorless", G-J are considered "near-colorless", K-M are "slightly colored". N-Y usually appear light yellow or brown.

In contrast to yellow or brown hues, diamonds of other colors are more rare and valuable. While even a pale pink or blue hue may increase the value of a diamond, more intense coloration is usually considered more desirable and commands the highest prices. A variety of impurities and structural imperfections cause different colors in diamonds, including yellow, pink, blue, red, green, brown, and other hues. Diamonds with unusual or intense coloration are sometimes labeled "fancy" by the diamond industry. Intense yellow coloration is considered one of the fancy colors, and is separate from the color grades of white diamonds. Gemologists have developed rating systems for fancy colored diamonds, but they are not in common use because of the relative rarity of colored diamonds.

Main article: Diamond color

The most fine quality as per color grading is totally colorless which is Graded as "D" color diamond across the globe which means it is absolutely free from any color. The next is very slight traces of color which can be observed by any expert Diamond valuer/grading laboratory. However when studded in the jewelery these very light colored diamonds do not show any color or it is not possible to make out color shades. These are graded as E color or F color Diamonds. Diamonds which show very little traces of color are graded as G or H color diamonds. Slightly colored diamonds are graded as I or J or K color. A diamond can be found in any other color also other than colorless. Some of the color diamonds such as pink are very rare diamonds and are priceless.

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. Depending on the hue and intensity of a diamond's coloration, a diamond's color can either detract from or enhance its value. For example, most white diamonds are discounted in price as more yellow hue is detectable, while intense pink or blue diamonds (such as the Hope Diamond) can be dramatically more valuable. The Aurora Diamond Collection displays a spectacular array of naturally colored diamonds.

Grading white diamonds

The majority of diamonds that are mined are in a range of pale yellow or brown color that is termed the normal color range. Diamonds that are of intense yellow or brown, or any other color are called fancy color diamonds. Diamonds that are of the very highest purity are totally colorless, and appear a bright white. The degree to which diamonds exhibit body color is one of the four value factors by which diamonds are assessed.

[edit] History of color grading

Color grading of diamonds was performed as a step of sorting rough diamonds for sale by the London Diamond Syndicate.

As the diamond trade developed, early diamond grades were introduced by various parties in the diamond trade. Without any co-operative development these early grading systems lacked standard nomenclature, and consistency. Some early grading scales were; I, II, III; A, AA, AAA; A, B, C. Numerous terms developed to describe diamonds of particular colors: golconda, river, jagers, cape, blue white, fine white, and gem blue, "brown"

Diamond color From Wikipedia, the free encyclopedi

Type II diamonds have no measurable nitrogen impurities. Type II diamonds absorb in a different region of the infrared, and transmit in the ultraviolet below 225 nm, unlike Type I diamonds. They also have differing fluorescence characteristics, but no discernible visible absorption spectrum. Type IIa diamond can be colored pink, red, or brown due to structural anomalies arising through plastic deformation during crystal growth—these diamonds are rare (1.8 percent of gem diamonds), but constitute a large percentage of Australian production. Type IIb diamonds, which account for 0.1 percent of gem diamonds, are usually a steely blue or grey due to scattered boron within the crystal matrix; these diamonds are also semiconductors, unlike other diamond types (see Electrical properties of diamond). However, an overabundance of hydrogen can also impart a blue color; these are not necessarily Type IIb.

Also not restricted to type are green diamonds, whose color is derived from exposure to varying quantities of radiation.

Possible colors Main article: Diamond type

Diamonds occur in a variety of colors — steel gray, white, blue, yellow, orange, red, green, pink to purple, brown, and black. Colored diamonds contain interstitial impurities or structural defects that cause the coloration, whilst pure diamonds are perfectly transparent and colorless. Diamonds are scientifically classed into two main types and several subtypes, according to the nature of impurities present and how these impurities affect light absorption:

Type I diamond has nitrogen (N) atoms as the main impurity, commonly at a concentration of 0.1 percent. If the N atoms are in pairs they do not affect the diamond's color; these are Type IaA. If the N atoms are in large even-numbered aggregates they impart a yellow to brown tint (Type IaB). About 98 percent^{[citation needed]} of gem diamonds are type Ia, and most of these are a mixture of IaA and IaB material: these diamonds belong to the Cape series, named after the diamond-rich region formerly known as Cape Province in South Africa, whose deposits are largely Type Ia. If the N atoms are dispersed throughout the crystal in isolated sites (not paired or grouped), they give the stone an intense yellow or occasionally brown tint (Type Ib); the rare canary diamonds belong to this type, which represents only 0.1 percent of known natural diamonds. Synthetic diamond containing nitrogen is Type Ib. Type I diamonds absorb in both the infrared and ultraviolet region, from 320 nm. They also have a characteristic fluorescence and visible absorption spectrum (see Optical properties of diamond).

Aurora Butterfly of Peace From Wikipedia, the free encyclopedia

Two research studies involving the Butterfly of Peace have resulted in new scientific breakthroughs about fluorescence and phosphorescence in fancy colored diamonds. The amazing phenomena of fluorescence can be seen as a skeletal pattern of glowing colors when the diamonds are exposed to ultraviolet light. There are rare and unusual color diamonds that make up the design including purples from Russia, blues and oranges from South Africa, lime greens from Brazil, violets and dozens of pinks from the Argyle Mine in Australia.

Aurora Butterfly of Peace From Wikipedia, the free encyclopedia

The Aurora Butterfly of Peace diamond collection is an artwork consisting of 240 natural, fancy colored diamonds weighing a combined total of 167 carats (33 g). This butterfly-shaped diamond mosaic was created over a period of twelve years by Alan Bronstein and Harry Rodman. The diamonds were collected and assembled one stone at a time. The Aurora Butterfly of Peace was conceived by the artists as an eternal icon of love, beauty, energy, nature, peace. It symbolizes a spiritual connection to earth for all mankind.

From November 2004 through July 2005, the Butterfly of Peace was exhibited in the National Gem Collection Gallery at the Smithsonian Institution in Washington, D.C.

A smaller version of the Butterfly of Peace was displayed at the Houston Museum of Natural Science from June 1994 through March 1996. The Aurora Butterfly of Peace was on display from May 25 to July 30, 2008 at the Museum of the Gemological Institute of America (GIA), to help launch “The Facets of the GIA” exhibit, which showcases the prominent role of the Institute in the world of gemology.

Simulants Main article: Diamond simulant

A diamond simulant is defined as a non-diamond material that is used to simulate the appearance of a diamond. Diamond-simulant gems are often referred to as diamante. The most familiar diamond simulant to most consumers is cubic zirconia. The popular gemstone moissanite (silicon carbide) is often treated as a diamond simulant, although it is a gemstone in its own right. While moissanite does look similar to diamond, its main disadvantage as a diamond simulant is that cubic zirconia is far cheaper and arguably equally convincing. Both cubic zirconia and moissanite are produced synthetically.^[87]

Synthetics

Another popular method of growing synthetic diamond is chemical vapor deposition (CVD). The growth occurs under low pressure (below atmospheric pressure). It involves feeding a mixture of gases (typically 1 to 99 methane to hydrogen) into a chamber and splitting them to chemically active radicals in a plasma ignited by microwaves, hot filament, arc discharge, welding torch or laser.^[85] This method is mostly used for coatings, but can also produce single crystals several millimeters in size (see picture).^[39]

At present, the annual production of gem quality synthetic diamonds is only a few thousand carats, whereas the total production of natural diamonds is around 120 million carats. Despite this fact, a purchaser is more likely to encounter a synthetic when looking for a fancy-colored diamond because nearly all synthetic diamonds are fancy-colored, while only 0.01% of natural diamonds are fancy-colored.^[86]

Synthetics Main article: Synthetic diamond

Synthetic diamonds are diamond crystals that are manufactured in a laboratory, as opposed to natural diamonds which form naturally within the Earth. The gemological and industrial uses of diamond have created a large demand for rough stones. This demand has been satisfied in large part by synthetic diamonds, which have been manufactured by various processes for more than half a century. However, in recent years it has become possible to produce gem-quality synthetic diamonds of significant size.^[33]

The majority of commercially available synthetic diamonds are yellow in color and produced by so called High Pressure High Temperature (HPHT) processes.^[83] The yellow color is caused by nitrogen impurities. Other colors may also be reproduced such as blue, green or pink, which are a result of the addition of boron or from irradiation after synthesis.^[84]

Cutting

The mined rough diamonds are converted into gems through a multi-step process called "cutting". Diamonds are extremely hard, but also brittle and can be split up by a single blow. Therefore, the diamond cutting is traditionally considered as a delicate procedure requiring skills, scientific knowledge, tools and experience. Its final goal is to produce a facetted jewel where the specific angles between the facets would optimize the diamond luster, that is dispersion of white light, whereas the number and area of facets would determine the weight of the final product. The weight reduction upon cutting is significant and can be of the order of 50%.^[42] Several possible shapes are considered, but the final decision is often determined not only by scientific, but also practical considerations. For example the diamond might be intended for display or for wear, in a ring or a necklace, singled or surrounded by other gems of certain color and shape.^[76]

The most time-consuming part of the cutting is the preliminary analysis of the rough stone. It needs to address a large number of issues, bears much responsibility, and therefore can last years in case of unique diamonds. The following issues are being considered:

• The hardness of diamond and its ability to cleave strongly depend on the crystal orientation. Therefore, the crystallographic structure of the diamond to be cut is analyzed using X-ray diffraction in order to choose the optimal cutting directions.
• Most diamonds contain visible non-diamond inclusions and crystal flaws. The cutter has to decide which flaws are to be removed by the cutting and which could be kept.
• The diamond can be split by a single, well calculated blow of a hammer to a pointed tool, which is quick, but risky. Alternatively, it can be cut with a diamond saw, which is a more reliable but tedious procedure.^[76][77]

After initial cutting, the diamond is shaped in numerous stages of polishing. Contrary to cutting, which is a responsible but quick operation, polishing removes material by gradual erosion and is extremely time consuming. However the associated technique is well developed; it is considered as a routine and can be performed by technicians.^[78] After polishing, the diamond is reexamined for possible flaws, either remaining or induced by the process. Those flaws are concealed through various diamond enhancement techniques, such as repolishing, crack filling, or clever arrangement of the stone in the jewelry. Remaining non-diamond inclusions are removed through laser drilling and filling of the produced voids.^[14]

Gemstones and their distribution

A large trade in gem-grade diamonds exists. Unlike other commodities, such as most precious metals, there is a substantial mark-up in the retail sale of gem diamonds.^[55] There is a well-established market for resale of polished diamonds (e.g. pawnbroking, auctions, second-hand jewelry stores, diamantaires, bourses, etc.). One hallmark of the trade in gem-quality diamonds is its remarkable concentration: wholesale trade and diamond cutting is limited to just a few locations; 92% of diamond pieces cut in 2003 were in Surat, Gujarat, India.^[56] Other important centers of diamond cutting and trading are Antwerp, where the International Gemological Institute is based, London, New York City, Tel Aviv, and Amsterdam. A single company—De Beers—controls a significant proportion of the trade in diamonds.^[57] They are based in Johannesburg, South Africa and London, England. One contributory factor is the geological nature of diamond deposits: several large primary kimberlite-pipe mines each account for significant portions of market share (such as the Jwaneng mine in Botswana, which is a single large pit operated by De Beers that can produce between 12.5 to 15 million carats of diamonds per year^[58]), whereas secondary alluvial diamond deposits tend to be fragmented amongst many different operators because they can be dispersed over many hundreds of square kilometers (e.g., alluvial deposits in Brazil).

The production and distribution of diamonds is largely consolidated in the hands of a few key players, and concentrated in traditional diamond trading centers. The most important being Antwerp, where 80% of all rough diamonds, 50% of all cut diamonds and more than 50% of all rough, cut and industrial diamonds combined are handled.^[59] This makes Antwerp a de facto "world diamond capital". Another important diamond center is New York City, where almost 80% of the world's diamonds are sold, including auction sales.^[59] The DeBeers company, as the world's largest diamond miner holds a dominant position in the industry, and has done so since soon after its founding in 1888 by the British imperialist Cecil Rhodes. De Beers owns or controls a significant portion of the world's rough diamond production facilities (mines) and distribution channels for gem-quality diamonds. The Diamond Trading Company (DTC) is a subsidiary of De Beers and markets rough diamonds from De Beers-operated mines. De Beers and its subsidiaries own mines that produce some 40% of annual world diamond production. For most of the 20th century over 80% of the world's rough diamonds passed through De Beers,^[60] but in the period 2001–2009 the figure has decreased to around 45%.^[61] De Beers sold off the vast majority its diamond stockpile in the late 1990s – early 2000s^[62] and the remainder largely represents working stock (diamonds that are being sorted before sale).^[63] This was well documented in the press^[64] but remains little known to the general public.

As a part of reducing its influence, De Beers withdrew from purchasing diamonds on the open market in 1999 and ceased, at the end of 2008, purchasing Russian diamonds mined by the largest Russian diamond company Alrosa.^[65] Alrosa however had to suspend their sales in October 2008 due to the global energy crisis and is expected to resume them in autumn 2009.^[66] Apart from Alrosa, other important diamond mining companies include BHP Billiton, which is the world's largest mining company;^[67] Rio Tinto Group, the owner of Argyle (100%), Diavik (60%), and Murowa (78%) diamond mines;^[68] and Petra Diamonds, the owner of several major diamond mines in Africa.

Further down the supply chain, members of The World Federation of Diamond Bourses (WFDB) act as a medium for wholesale diamond exchange, trading both polished and rough diamonds. The WFDB consists of independent diamond bourses in major cutting centers such as Tel Aviv, Antwerp, Johannesburg and other cities across the USA, Europe and Asia.^[20] In 2000, the WFDB and The International Diamond Manufacturers Association established the World Diamond Council to prevent the trading of diamonds used to fund war and inhumane acts. WFDB's additional activities include sponsoring the World Diamond Congress every two years, as well as the establishment of the International Diamond Council (IDC) to oversee diamond grading.

Once purchased by Sightholders (which is a trademark term referring to the companies that have a three-year supply contract with DTC), diamonds are cut and polished in preparation for sale as gemstones ('industrial' stones are regarded as a by-product of the gemstone market; they are used for abrasives).^[69] The cutting and polishing of rough diamonds is a specialized skill that is concentrated in a limited number of locations worldwide.^[69] Traditional diamond cutting centers are Antwerp, Amsterdam, Johannesburg, New York City, and Tel Aviv. Recently, diamond cutting centers have been established in China, India, Thailand, Namibia and Botswana.^[69] Cutting centers with lower cost of labor, notably Surat in Gujarat, India, handle a larger number of smaller carat diamonds, while smaller quantities of larger or more valuable diamonds are more likely to be handled in Europe or North America. The recent expansion of this industry in India, employing low cost labor, has allowed smaller diamonds to be prepared as gems in greater quantities than was previously economically feasible.^[59]

Diamonds which have been prepared as gemstones are sold on diamond exchanges called bourses. There are 26 registered diamond bourses in the world.^[70] Bourses are the final tightly controlled step in the diamond supply chain; wholesalers and even retailers are able to buy relatively small lots of diamonds at the bourses, after which they are prepared for final sale to the consumer. Diamonds can be sold already set in jewelry, or sold unset ("loose"). According to the Rio Tinto Group, in 2002 the diamonds produced and released to the market were valued at US$9 billion as rough diamonds, US$14 billion after being cut and polished, US$28 billion in wholesale diamond jewelry, and US$57 billion in retail sales.^[71]

Formation in cratons

Through studies of carbon isotope ratios (similar to the methodology used in carbon dating, except with the stable isotopes C-12 and C-13), it has been shown that the carbon found in diamonds comes from both inorganic and organic sources. Some diamonds, known as harzburgitic, are formed from inorganic carbon originally found deep in the Earth's mantle. In contrast, eclogitic diamonds contain organic carbon from organic detritus that has been pushed down from the surface of the Earth's crust through subduction (see plate tectonics) before transforming into diamond. These two different source of carbons have measurably different ¹³C:¹²C ratios. Diamonds that have come to the Earth's surface are generally quite old, ranging from under 1 billion to 3.3 billion years old. This is 22% to 73% of the age of the Earth.^[33]

Diamonds occur most often as euhedral or rounded octahedra and twinned octahedra known as macles. As diamond's crystal structure has a cubic arrangement of the atoms, they have many facets that belong to a cube, octahedron, rhombicosidodecahedron, tetrakis hexahedron or disdyakis dodecahedron. The crystals can have rounded off and unexpressive edges and can be elongated. Sometimes they are found grown together or form double "twinned" crystals at the surfaces of the octahedron. These different shapes and habits of the diamonds result from differing external circumstances. Diamonds (especially those with rounded crystal faces) are commonly found coated in nyf, an opaque gum-like skin.^[34]

Color

Diamond has a wide bandgap of 5.5 eV corresponding to the deep ultraviolet wavelength of 225 nanometers. This means pure diamond should transmit visible light and appear as a clear colorless crystal. Colors in diamond originate from lattice defects and impurities. The diamond crystal lattice is exceptionally strong and only atoms of nitrogen, boron and hydrogen can be introduced into diamond during the growth at significant concentrations (up to atomic percents). Transition metals Ni and Co, which are commonly used for growth of synthetic diamond by the high-pressure high-temperature techniques, have been detected in diamond as individual atoms, however the maximum concentration is 0.01% for Ni^[24] and even much less for Co. Note however, that virtually any element can be introduced in diamond by ion implantation.^[25]

Nitrogen is by far the most common impurity found in gem diamonds. Nitrogen is responsible for the yellow and brown in diamonds. Boron is responsible for the gray blue colors.^[11] Color in diamond has two additional sources: irradiation (usually by alpha particles), that causes the color in green diamonds; and physical deformation of the diamond crystal known as plastic deformation. Plastic deformation is the cause of color in some brown^[26] and perhaps pink and red diamonds.^[27] In order of rarity, colorless diamond, by far the most common, is followed by yellow and brown, by far the most common colors, then by blue, green, black, translucent white, pink, violet, orange, purple, and the rarest, red.^[20] "Black", or Carbonado, diamonds are not truly black, but rather contain numerous dark inclusions that give the gems their dark appearance. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent and colorless. Most diamond impurities replace a carbon atom in the crystal lattice, known as a carbon flaw. The most common impurity, nitrogen, causes a slight to intense yellow coloration depending upon the type and concentration of nitrogen present.^[20] The Gemological Institute of America (GIA) classifies low saturation yellow and brown diamonds as diamonds in the normal color range, and applies a grading scale from "D" (colorless) to "Z" (light yellow). Diamonds of a different color, such as blue, are called fancy colored diamonds, and fall under a different grading scale.^[20]

In 2008, the Wittelsbach Diamond, a 35.56 carats (7.11 g) blue diamond once belonging to the King of Spain, fetched over US$24 million at a Christie's auction.^[28] In 2009 a 7.03 carats (1.41 g) blue diamond fetched the highest price per-carat ever paid for a diamond when it was sold at auction for 10.5 million Swiss francs (6.97 million Euro or US$9.5 million at the time) which is in excess of US$1.3 million per carat.^[29]

Material properties

A diamond is a transparent crystal of tetrahedrally bonded carbon atoms (sp³) that crystallizes into the diamond lattice which is a variation of the face centered cubic structure. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness and thermal conductivity (900–2,320 W·m⁻¹·K⁻¹),^[10] as well as wide bandgap and high optical dispersion.^[11] Above 1,700 °C (1,973 K / 3,583 °F) in vacuum or oxygen-free atmosphere, diamond converts to graphite; in air, transformation starts at ~700 °C.^[12] Naturally occurring diamonds have a density ranging from 3.15–3.53 g/cm³, with very pure diamond typically extremely close to 3.52 g/cm³.^[1] Despite the hardness of diamonds, the chemical bonds that hold the carbon atoms in diamonds together are actually weaker than those that hold together the other form of pure carbon, graphite. The difference is that in diamonds, the bonds form an inflexible three-dimensional lattice. In graphite, the atoms are tightly bonded into sheets, which can slide easily however.^[13]

Diamond

In mineralogy, diamond (from the ancient Greek adámas, meaning "proper" or "unalterable") is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is the second most stable form of carbon, after graphite; however, the conversion rate from diamond to graphite is negligible at ambient conditions. Diamond is specifically renowned as a material with superlative physical qualities, most of which originate from the strong covalent bonding between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material synthesized so far. Those properties determine the major industrial application of diamond in cutting and polishing tools.

Diamond has remarkable optical characteristics. Because of its extremely rigid lattice, it can be contaminated by only few types of impurities, such as boron and nitrogen. Combined with the wide transparency, this results in clear, colorless appearance of most natural diamonds. Small amounts of defects or impurities (about one per million of lattice atoms) color diamond blue (boron), yellow (nitrogen), brown (lattice defects), green, purple, pink, orange or red. Diamond also has relatively high optical dispersion, that is ability to disperse light of different colors, which results in its characteristic luster. Excellent optical and mechanical properties, combined with efficient marketing, make diamond the most popular gemstone.

Most natural diamonds are formed at high-pressure high-temperature conditions existing at depths of 140 to 190 kilometers (87 to 120 mi) in the Earth mantle. Carbon-containing minerals provide the carbon source, and the growth occurs over periods from 1 billion to 3.3 billion years, which respectively corresponds to roughly 25% and 75% of the age of the Earth. Diamonds are brought close to the Earth surface through deep volcanic eruptions by a magma, which cools into igneous rocks known as kimberlites and lamproites. Diamonds can also be produced synthetically in a high-pressure high-temperature process which approximately simulates the conditions in the Earth mantle. An alternative, and completely different growth technique is chemical vapor deposition. Several non-diamond materials, which include cubic zirconia and silicon carbide and are often called diamond simulants, resemble diamond in appearance and many properties. Special gemological techniques have been specially developed to distinguish natural and synthetic diamonds and diamond simulants.