Diamond

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Alternate meanings: Diamond (disambiguation)
Diamond
A scattering of "brilliant" cut diamonds shows off the many reflecting facets.
General
Category Native Nonmetal, Mineral
Chemical formula Carbon, C
Identification
Color Most often colorless to white. Rarely pink, yellow, orange, green or blue.
Crystal habit Octahedral, spherical or massive
Crystal system Isometric
Cleavage Octahedral
Fracture Conchoidal
Mohs Scale hardness 10
Luster Adamantine to greasy
Refractive index 2.417
Pleochroism None
Streak None
Specific gravity 3.516 - 3.525
Fusibility ?
Solubility ?
Major varieties
None

Diamond is one of the natural allotropes of carbon (the main allotrope being graphite; see also allotropes of carbon). The hardest of naturally occurring materials, diamonds cut into multi-faceted shapes are among the most prized gemstones of jewelry, and find use in industrial applications as well.

Material properties

Main article: Material properties of diamond

Diamond is a transparent crystal of pure carbon consisting of tetrahedrally bonded carbon atoms. Humans have been able to adapt diamonds for many uses because of the material's exceptional physical characteristics. Most notable among these properties are the extreme hardness of diamond and its high dispersion index. These two properties form the basis for most modern applications of diamond.

File:Diamsm.gif
The diamond crystal bond structure gives the gem its hardness and differentiates it from graphite.

Mechanical properties

Crystal structure: Diamonds typically crystallize in the cubic crystal system and consist of tetrahedrally bonded carbon atoms. A rare second form called lonsdaleite has hexagonal symmetry. The tetrahedral arrangement of atoms in a diamond crystal is the source of many of diamond's properties; graphite, another allotrope of carbon, has a rhombohedral crystal structure and as a result shows dramatically different physical characteristics.

Hardness: Diamond is the hardest known naturally occurring material, scoring 10 on the relative Mohs scale of mineral hardness and having an absolute hardness value of between 167 and 231 gigapascals in various tests.

Broad industrial applications of diamond are based on the extraordinary hardness of diamond. As the hardest known naturally occurring material, diamond can be used to polish, cut, or wear away any material, including other diamonds. Common industrial adaptations of this ability include diamond-tipped drill bits and saws.

The hardness of diamonds also contributes to its suitability as a gemstone. Because it can only be scratched by other diamonds, it maintains its polish extremely well, keeping its luster over long periods of time. Unlike many other gems, it is well-suited to daily wear due to its resistance to scratching — perhaps contributing to its popularity as the preferred gem in an engagement ring or wedding ring, which are often worn every day.

Diamond's hardness has been known since antiquity, and is the source of its name. The diamond derives its name from the Greek adamas, meaning "untameable" or "unconquerable", referring to its hardness.

Toughness: Unlike hardness, which only denotes resistance to scratching, diamond's toughness is only fair to good. Toughness relates to a material's ability to resist breakage from forceful impact. As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Diamonds cut into certain particular shapes are therefore more prone to breakage than others.

Color: Diamonds occur in a variety of transparent hues — colorless, white, steel, blue, yellow, orange, red, green, pink, brown — or colored black. Diamonds with a detectable hue to them are known as colored diamonds. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly-pure diamonds are be transparent and colorless. Most diamond impurities replace a carbon atom in the crystal lattice. The most common impurity, nitrogen, causes a yellowish or brownish tinge.

Natural occurence: Diamonds occur most often as euhedral or rounded octahedra and twinned octahedra known as macles. Other forms include dodecahedra and cubes. Diamonds are commonly found coated in nyf, a gum-like skin.

Thermodynamic stability: At surface air pressure (one atmosphere), diamonds are not as stable as graphite, and so the decay of diamond is thermodynamically favorable (δH = −2 kJ / mol). Diamonds have been shown to burn in the late 18th century, and previously during Roman times. So, despite the popular advertising slogan, diamonds are definitely not forever. However, owing to a very large kinetic energy barrier, diamonds are metastable; they will not decay into graphite under normal conditions.

Electromagnetic properties

Optical properties: Diamonds exhibit a high dispersion of visible light. This strong ability to split white light into its component colors is an important aspect of diamond's attraction as a gemstone, giving it impressive prismatic action that results in so-called fire in a well-cut stone. The luster of a diamond is described as adamantine, which simply means diamond-like. Some diamonds exhibit fluorescence of various colors under long wave ultraviolet light, but generally show bluish-white, yellowish or greenish fluorescence under X-rays. Some diamonds show no fluorescence.

Electrical properties: Except for most natural blue diamonds which are semiconductors, diamond is a good electrical insulator. Blue diamonds owe their semiconductive property to boron impurities, which act as a doping agent and cause p-type semiconductor behavior. Natural blue diamonds which are not boron-doped, such as those recently recovered from the Argyle mine in Australia that owe their color to an overabundance of hydrogen atoms, are not semiconductors.

Thermal properties: Unlike most electrical insulators, diamond is a good conductor of heat because of the strong covalent bonding within the crystal. Most natural blue diamonds contain boron atoms which replace carbon atoms in the crystal matrix, and also have high thermal conductance. Specially purified synthetic diamond has the highest thermal conductivity (2000–2500 W/(m·K), five times more than copper) of any known solid at room temperature. Because diamond has such high thermal conductance it is already used in semiconductor manufacture to prevent silicon and other semiconducting materials from overheating.

The diamond industry

Only diamonds are hard enough to cut other diamonds. Polishing and mounting add further value, brilliance, and appeal as jewelry.

Due to their high dispersion and unsurpassed hardness, diamonds have long been prized as a constituent of jewellery. A large trade in gem-grade diamonds exists, mostly controlled by the De Beers company, which has used its monopoly to manipulate prices. Unlike precious metals such as gold or platinum, there is a substantial mark-up in the sale of diamonds and there is not a very active market for resale of diamonds, making them rather unsuitable as investments or as a store of value.

At one time it was thought over 80% of the world's rough diamonds passed through the Diamond Trading Company (DTC, a subsidiary of De Beers) in London, but presently the figure is estimated at c. 60%. In the late '90s, Canadian prospectors discovered several rich sources of diamonds. For example, the Ekati Diamond Mine, which was opened in 1998, produces 3 million carats (600 kg) of rough diamond every year. The Diavik Diamond Mine was opened in 2004.

Diamonds are valued according to the four C's of diamond grading, namely cut, clarity, color, and carat. Both rough and cut diamonds are graded and separated based on these four characteristics at a number of heavily guarded grading centers, such as the DTC.

Cut

The history of diamond cutting can be traced to the late Middle Ages, before which time diamonds were enjoyed in their natural octahedral state. The first "improvements" on nature's design involved a polishing of the crystal faces—this was called the point cut. Later still, a little less than one half of the crystal would be sawn off, creating the table cut. Neither of these early cuts would reveal what diamond is prized for today; its strong dispersion or fire. At the time, diamond was valued chiefly for its brilliant lustre and superlative hardness; a table-cut diamond would appear black to the eye, as they do in paintings of the era.

In 1375, there was a guild of diamond polishers at Nürnberg.

In or around 1476 Lodewyk (Louis) van Berquem, a Flemish polisher of Bruges, introduced absolute symmetry in the disposition of facets. He cut stones in the shape known as pendeloque or briolette.

About the middle of the sixteenth century, the rose or rosette was introduced.

The brilliant cut was introduced in the middle of the seventeenth century. The first brilliants were known as Mazarins. They had 17 facets on the crown (upper half). They are called double-cut brilliants.

Vincent Peruzzi, a Venetian polisher, increased the number of crown facets from 17 to 33 (triple-cut brilliants), thereby increasing very much the fire and brilliancy of the cut gem, which were already in the double-cut brilliant incomparably better than in the rose. Yet diamonds of that cut, when seen nowadays, seem exceedingly dull compared to modern-cut ones.

File:Ideal cut dm.jpg
Light dispersion from an ideal cut diamond simulant. Notice the near-perfect symmetry of the light reflected out of the stone.

Roughly 1900, the development of diamond saws and good jewellery lathes enabled the development of modern diamond cuts, chief among them the round brilliant cut. In 1919, Marcel Tolkowsky analyzed this cut. His calculations took both brilliance (the amount of white light reflected) and fire into consideration, creating a delicate balance between the two. His geometric calculations can be found in his book on Diamond Design.

The modern round brilliant consists of 58 facets (or 57 if the culet is excluded); 33 on the crown (the top half above the middle or girdle of the stone) and 25 on the pavilion (the lower half below the girdle). In recent decades, most girdles are faceted. Many girdles have 32, 64, 80, or 96 facets; these facets are not counted in the total. While the facet count is standard, the actual proportions (crown height and angle, pavilion depth, etc.) are not universally agreed upon. One may speak of the American cut or the Scandinavian standard (Scan. D.N.), to give but two examples.

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%. 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.

Popular fancy cuts include the baguette (from the French, resembling a loaf of bread), marquise or navette ("little boat"), princess (square outline), heart, briolette (a form of the rose cut), and the pear or drop cuts. Generally speaking, these "fancy cuts" are not held to the same strict standards as Tolkowsky-derived round brilliants. Cuts are influenced heavily by fashion; baguettes—which accentuate a diamond's lustre and downplay its fire—were all the rage during the Art Deco period, whereas the princess cut—which accentuates a diamond's fire rather than its lustre—is currently gaining popularity. The princess cut is also popular amongst diamond cutters: of all the cuts, it wastes the least of the original crystal.

In the 1970s, Bruce Harding developed another mathematical model for gem design. Since then, several groups have used computer models (e.g., MSU, OctoNus, GIA, and folds.net) and specialized scopes to design diamond cuts.

During the 1990s Israeli interests, centralized in Ramat Gan, acquired about 20% of the diamond trade, buying diamonds from Russia and from mines in Africa not controlled by De Beers. De Beers now deals only in diamonds from their own mines. A major diamond cutting industry has grown up in the state of Gujarat, India where 90% of the world's diamonds (as measured by number of diamonds) are cut by a workforce of 800,000[1]. Small diamonds previously not worth cutting are cut in India, opening up a new market segment for small diamonds.

Some cuts are:

  • Round
  • Radiant
  • Pear
  • Marquise
  • Emerald
  • Oval
  • Heart
  • Princess

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. As far as the shape of the cut is concerned, it is very much a personal taste and preference. However, when jewelers judge the quality of a cut diamond, they often rate "Cut" as the most important of the "4-Cs." The key is not the shape, but how well the cutters executed that shape. The proportion, symmetry and quality of the polish are essential criteria of a good cut. Since the "brilliance" and "fire" of a diamond depends very much on the angle of the facets in relation to each other. A poorly cut diamond with facets cut only a few degrees from optimal will result in a stone that lacks the gem quality. For a round brilliant cut, there is a balance between "brilliance" and "fire". When a diamond is cut for too much "fire", it would look like a cubic zirconia which gives out much more "fire" than real diamond. A well executed round brilliant cut should reflect most light out from the tabletop and make the diamond appear white when viewed from the top. An inferior cut will produce a stone that appears dark at the center and in some extreme cases the ring settings may show through the top of the diamond as shadows.

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 is much higher when the stone is over one 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 carat diamond for its better price or buy a 1.10 carat diamond for its better cut. A 1.00 carat diamond is usually poorly cut stone.

Cut grading

The "Cut" of the "4-Cs" is the most difficult part for a consumer to choose in selecting a good diamond because a GIA certificate will not show the important measurements influencing cut (i.e. pavilon and crown angle) and will not provide a subjective ranking of how good the cut was. The other 3-Cs can be ranked simply by the rating in each category. It requires a trained eye to see the quality of a good "cut".

Several groups have developed diamond cut grading standards.

  • The AGA standards may be the strictest. David Atlas (who developed the AGA standards) has suggested that they are overly strict.
  • The HCA changed several times between 2001 and 2004. As of 2004, an HCA score below two represented an excellent cut. The HCA distinguishes between brilliant, Tolkowsky, and fiery cuts.
  • The AGS standards will change in the first quarter of 2005 to better match Tolkowsky's model and Octonus' ray tracing results.

The distance from the viewer's eye to the diamond is important. The 2005 AGS cut standards are based on a distance of 25 centimeters (about 10 inches). The 2004 HCA cut standards are based on a distance of 40 centimeters (about 16 inches).

Clarity

Clarity is a measure of internal structural imperfections called "inclusions". Grades of clarity, which are mostly those used by Gemological Institute of America (GIA), are:

  • FL - "flawless" in that no inclusions are visible under 10 times magnification
  • IF - "internally flawless" with no inclusions visible under 10 times magnification, only small blemishes
  • VVS1 and VVS2 - "very very small" inclusions that are difficult to see under 10 times magnification. VVS1 is a better grade than VVS2.
  • VS1 and VS2 - "very small" inclusions and visible under magnification but invisible to the naked eye.
  • SI1 and SI2 - "small inclusions" that can be noticeable to the naked eye, if you know where to look.
  • "SI3" is a grade sometimes used in the industry, originally popularized by the European Gemological Laboratory (EGL) Los Angeles grading office. While theoretically a range including lower SI2 and upper I1, it's commonly used to mean I1's which are "eye clean", that is, which have inclusions which aren't readily visible to the naked eye. Neither the GIA nor the American Gemological Society (AGS), the most reputable well known US labs, assign this grade.
  • I1, I2 and I3 - "imperfect" and visible to the naked eye. For I3, the inclusions impact the brilliance of the diamond and are large and obvious.

All grades reflect the appearance to an experienced grader when viewed from above at 10x magnification, though higher magnifications and viewing from other angles are used during the grading process. In "colorless" diamonds, dark inclusions will tend to create the greatest drop of clarity grade. In other colors pale inclusions may have greater relief (may stand out more) and may cause a greater drop in grade.

Beyond the clarity grading terms, other considerations include the type, size and location of the "inclusion". Inclusions near or on the surface may weaken the diamond structurally. Depending on where the inclusion occurs in the cut diamond and how it is to be used, it may be possible to hide the inclusion behind the setting.

Laser "drilling" involves using a laser to burn a hole to a colored inclusion, followed by acid washing to remove the coloring agent. The clarity grade is the grade after the treatment. The treatment is considered permanent and both the GIA and AGS will issue grades for laser drilled diamonds. Reputable vendors should disclose that laser drilling has been used.

Clarity can also be "enhanced" by filling the fracture much like a car windshield crack can be treated. Such diamonds are sometimes called "fracture filled diamonds". Reputable vendors must disclose this filling and reputable filling companies use filling agents which show a flash of color, commonly orange or pink, when viewed closely. There is a significant price discount for fracture-filled diamonds. The GIA will not grade fracture-filled diamonds, in part because the treatment isn't as permanent as diamond. Reputable companies often provide for repeat treatments if heat causes damage to the filling. The heat required to cause damage is that of a blowtorch used to work on settings, and it is essential to inform anyone working on a setting if the diamond is fracture-filled, so they can apply cooling agents to the diamond and use greater care while working on it.

Color

Jewelers set diamonds in groups of similar colors.

The Gemological Institute of America uses as "D" to "Z" scale for color where "D" is colorless and "Z" is yellow:

  • colorless: D, E, F
  • near colorless: G, H, I, J
  • faint yellow or brown: K, L, M
  • very light yellow or brown: N, O, P, Q, R
  • light yellow or brown: S, T, U, V, W, X, Y, Z

Colorless diamonds are priced higher than yellow diamonds. However, when a diamond's color is more intense than the "Z" grading, it enters the realm of "Fancy Color". In this case, the intensity of the color in the diamond plays a major role in its value. The value of a Fancy Color Diamond may far surpass that of colorless diamonds, if the intensity of the color is high and the color is rare. A diamond may come in all colors of the rainbow.

Yellow color is caused by nitrogen atoms trapped in the crystal.

A fancy brown diamond may have low value, relative to colorless diamond. However, a fancy pink or blue diamond will command higher prices. Fancy-colored diamonds such as the deep blue Hope Diamond are particularly valuable.

Brown rather than yellow as the color became more common as Australian diamonds entered the market and is generally less appreciated by consumers and sold at a greater discount if the color is readily visible.

80% of the diamonds produced are poorer quality (discolored, less transparent) diamonds called bort which are used as industrial diamonds, where their extreme hardness is useful in cutting and grinding otherwise intractable materials (including other diamonds). Lately, gas-phase deposition processes have been devised that allow thin diamond films to be grown on some surfaces, greatly increasing the durability of some machine tools.

While the prices are higher for colorless diamonds, the exact color most valued by a consumer is a matter of personal preference, with some preferring the very transparent D-F range, while others prefer the "warmer" colors in the G-J range and still others prefer a clearly visible tint.

Sources

Historically diamonds were found in alluvial deposits in southern India which are now worked out. Most diamond deposits are in Africa, notably in South Africa, Namibia, Botswana, the Republic of the Congo and Sierra Leone. Revolutionary groups in some of those countries have taken control of diamond mines, using the conflict diamonds to finance their operations. In response to public concerns that their diamond purchases were contributing to war and human rights abuses in central Africa, the diamond industry and diamond-trading nations introduced the Kimberley Process aimed at ensuring that conflict diamonds do not becoming intermixed with the diamonds not controlled by such rebel groups.

There are also commercial deposits in the Northwest Territories of Canada, the Russian Arctic, Brazil and in Northern and Western Australia. Occasionally diamonds have been found in glacial deposits in Wisconsin and Indiana. The Wisconsin finds can be explained by recent Canadian discoveries, but the diamonds found in Indiana must have come from an as yet undiscovered source in Quebec as the movement of ice was from northeast to southwest. There is also a diamond mine at Crater of Diamonds State Park in Murfreesboro, Arkansas. Tiny nanometre-sized diamonds, often called nanodiamonds, are also found as presolar grains in primitive meteorites.

Diamonds have been manufactured synthetically for over fifty years, and very recently companies began marketing them to the public as jewelry and in technology. For more information see Synthetic diamond.

A city of major importance in diamond trade is Antwerp, Belgium. It is estimated that nearly 90% of the world's rough diamonds, 50% of cut diamonds, and 40% of industrial diamonds trade hands in Antwerp. The industry is represented by the Diamond High Council (HRD). Before Antwerp the port city of Bruges saw most diamond trade, holding its position since the 13th century. Toward the 15th century Bruges declined, its port choked with silt.

Antwerp had been the world centre of diamond trade since the 16th century, until the city's 1585 capture by the Spanish. Amsterdam then supplanted Antwerp as a trading centre, until the latter's resurgence beginning in the 19th century.

Symbolism

It is said the Greeks believed diamonds were tears of the gods; the Romans believed they were splinters of fallen stars. Many long dead cultures have sought the divine or the mystical in diamond, thereby explaining its specialities.

Perhaps the earliest symbolic use of diamonds was as the eyes of Hindu devotional statues. The diamonds themselves were thought to be endowments from the gods and were therefore cherished. The point at which diamonds assumed their divine status is not known, but early texts indicate they were recognized in India since at least 400 BC.

In western culture, diamonds are the traditional emblem of fearlessness and virtue. Although rarely seen in jewellery prior to the Baroque period, early examples of betrothal jewels incorporating diamonds include the Bridal Crown of Blanche (ca. 1370-1380) and the Heftlein brooch of Vienna (ca. 1430-1440), a pictorial piece depicting a wedding couple.

Today, diamonds are used to symbolize eternity and love, being often seen adorning engagement rings. This modern tradition can be directly traced to the marketing campaigns of De Beers, starting in 1938. These campaigns have included measures such as:

  • showing diamonds as wedding gifts in popular romantic movies
  • publishing stories in magazines and newspapers which would emphasize the romantic value of diamonds and associate them with celebrities
  • employing fashion designers and other trendsetters to promote the trend on radio and, later, television
  • enlisting the Royal Family of the United Kingdom to directly promote diamonds.

This campaign was described by De Beers' PR agency N. W. Ayer as "a new form of advertising which has been widely imitated ever since" with "no brand name to be impressed on the public mind. There was simply an idea -- the eternal emotional value surrounding the diamond." Indeed, the campaign succeeded in reviving the American diamond market, which had been weakened by "competitive luxuries", and in opening new markets where none had existed before. In Japan, for example, diamonds were successfully promoted as a western symbol of status, which coincided with Japan's cultural opening after World War II. Japan, which had no diamond tradition before the De Beers campaign, is today the second largest market for retail diamonds.

The slogan "A Diamond is Forever", invented by N.W. Ayer, is one of the most successful slogans in marketing history. Its purpose is to prevent the creation of a secondary market by dissuading women from selling the diamonds they have received and by discouraging them from buying diamonds which other women have owned. The consequence of this is that retailers can sell diamonds at a high price without competition from a secondary market and to allow DeBeers to maintain control of the diamond trade at the wholesale level.

The diamond engagement ring is, however, not an original invention of De Beers. It can be traced to the marriage of Maximilian I (then Archduke of Austria) to Mary of Burgundy in 1477. While the act did much to advance the Habsburg empire, it did little to make the diamond ring a widely encountered expression of betrothal.

The inception of the engagement ring itself can be tied to the Fourth Lateran Council presided over by Pope Innocent III in 1215. Innocent declared a longer waiting period between betrothal and marriage; plain rings of gold, silver or iron were used earliest. Gems were more than baubles; they were important and reassuring status symbols to the aristocracy. Laws were passed to preserve a visible division of social rank, ensuring only the privileged wore florid jewels. As time passed and laws relaxed, diamonds and other gems became obtainable to the middle class.

The diamond is considered the birthstone for people born in April.

The LifeGem company further taps modern symbolism by offering to synthetically convert the carbonized remains of people or pets into "memorial diamonds." However, many people still feel very uncomfortable at the thought of wearing the carbonized remains of people as jewelry.

Related terms

A 'schlenter' is Australian or South African mining slang for 'fake', that is, an imitation diamond.

Famous diamond cutters

Famous stones

See also

External links

Labs, cut, and general resources

  • OctoNus Software has posted several diamond cut studies, by various authors. OctoNus, Moscow State University, Bruce Harding, and others have posted work there.
  • Gemological Institute of America is the most widely recognized and trusted name in gemstone grading. A certificate from GIA is literally a guarantee of gemstone authenticity and quality.
  • European Gemological Laboratory a very popular lab amongst jewelers, faster turnaround for certification and your gemstone generally receives a less "strict" grading. They also provide appraisals for insurance purposes - a service that GIA does not provide.
  • Smithsonian's exhibit of fancy color diamonds
  • "The Nature of Diamonds" - American Museum of Natural History's online exhibition on diamonds. Detailed look at the history, art and science behind the stone.
  • PBS Nature: Diamonds
  • Adamas Gemological Laboratory makes spectrophotometer machines that measure the color of gems. The machines can be programmed to distinguish natural, artificial, and color-enhanced gems.

Chemistry and artificial diamonds

Natural sources and marketing

Further reading

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