DIAMOND HISTORY
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An extremely hard, highly refractive crystalline form of carbon that is usually colorless and is used as a gemstone and in abrasives, cutting tools, and other applications. A piece of jewelry containing such a gemstone. A figure with four equal sides forming two inner obtuse angles and two inner acute angles; a rhombus or lozenge. Games. A red, lozenge-shaped figure on certain playing cards. A playing card with this figure. diamonds (used with a sing. or pl. verb) The suit of cards represented by this figure.
Baseball. An infield. The whole playing field.
adj.
Of or relating to a 60th or 75th anniversary.
tr.v., -mond·ed, -mond·ing, -monds.
To adorn with or as if with diamonds.
idiom:
diamond in the rough One having exceptionally good qualities or the potential for greatness but lacking polish and refinement.
[Middle English diamaunt, from Old French diamant, from Medieval Latin diamās-, diamant-, alteration of Latin adamās. See adamant.]
How Products are Made: How is a diamond made? Background
The diamond is the hardest natural substance known. It is found in a type of igneous rock known as kimberlite. The diamond itself is essentially a chain of carbon atoms that have crystallized. The stone's unique hardness is a result of the densely concentrated nature of the carbon chains. Like other igneous rocks, kimberlite was formed over the course of thousands of years by volcanic action that occurred during the formation of the earth's crust. Kimberlite is located inside these former spheres of volcanic activity—often near mountain ranges—in vertical shafts that extend deep inside the earth. Inside the kimberlite are intermittent deposits of diamonds, one of several minerals present. However, not all kimberlite contains diamond. Other stones often found with diamonds are mica, garnet, and zircon. Kimberlite may be blue-grey in hue—thus termed blue ground—or if exposed to air it may have a yellowish cast and is called yellow ground.
History
It is thought that diamonds were first discovered in Indiaabout 6,000 years ago in the riverbeds of the region. Traders were responsible for bringing the gems as far east as China and as far west as Rome during the classical and early medieval eras. The Chinese were the first to hamess the unusually tough nature of the gem and used it as a tool to cut other stones. Pliny the Elder, a Roman scholar, wrote about the diamond in the first century. The word itself stems from the Greek term adamas which means "invincible" or "unconquerable."
From the earliest days, the diamond has been imbued with mystery and superstition. Because they were so rare—at first found only in India—it became a commonly held superstition that the diamond lent its wearer special powers. They were worn in battle to insure victory and sometimes invoked as an antidote to poison. Other superstitions associated with the stone included the caveat that placing it in the mouth would bring on a loss of teeth. In other cases, finely ground diamond, made into a powder, was thought to be an effective poison. Indeed, experts agree that even in a pulverized form, the unique sharpness of the mineral would tear minuscule holes in the digestive tract. Because it is both the hardest and one of the rarest natural substances, diamonds have always fetched exceedingly high prices. The extreme value of the stone also made it a portable form of wealth in times of warfare and upheaval.
The actual mining of diamonds as an industry can be traced back to India to around 800 to 600 B.C. India was the only known source of the rocks for over a thousand years, until they were unearthed in Borneo around A.D. 600. During the Middle Ages, the diamond was overshadowed by some of the more colorful gems like the ruby and emerald. These other stones found their way into the jewelry of the rich and powerful of Europe more easily than the diamond. Additionally, gem-cutting techniques had not yet been developed to unleash the brilliance of the stone. Diamonds were usually left in their natural state or shaped by a rudimentary cut. In the 17th century, how-ever, a Venetian lapidary named Vincenzo Peruzzi developed the so-called brilliant cut. This cut revealed the intricacies and the natural perfection of the stone.
In the 18th century, diamond deposits were discovered in Brazil in small quantities, and later in Australia, Russia, and the United States. Brazilian gems were first taken to India and shipped to Europe as Indian diamonds, since people considered non-Indian gems less valuable. In the 20th century, an American mine near Murfreesboro, Arkansas, was open for novelty public mining for a small fee. High-quality diamonds have been found in Siberia, but the extremely cold temperature has made large-scale mining unfeasible.
In 1866 the world's largest cache of diamonds was discovered in South Africa. Some children had found a rock and brought it home, and a curious neighbor passed it on to a trader, who gave it to a geologist. It was discovered to be a diamond of enormous size and worth a small fortune. South Africa soon experienced a diamond rush, and shanty towns sprang up with the influx of prospectors. Eventually, the various mines and mine companies of the region were consolidated under the control of the DeBeers organization. With the DeBeers Consolidated Mines, Ltd., a Central Selling Organization, and a Diamond Trading Company, this conglomerate controls about 80% of the world's diamond output. Contemporary diamond mining is centered at Kimberley, South Africa, and carried out by DeBeers. Every six weeks or so, representatives of the DeBeers Diamond Trading Company invite a special list of diamond wholesalers—less than a hundred world-wide—to London to view preselected lots of the gem. This is the only method by which South African DeBeers diamonds come onto the market.
Industrial Applications
In modern times diamonds have become indispensable to industry. Automobile magnate Henry Ford was the first to uncover the contemporary industrial uses of the stone. He sponsored research into its applications for the manufacturing sector, especially as a low-cost abrasive, and the Detroit area became a hub for dealers of diamond tools. The aircraft industry followed the lead of the automotive sector, becoming an avid user of diamond-based products. Diamonds used for industrial applications are usually of a lower grade than those found in the gemstone market, but they retain the same properties of hardness and durability. Diamond tools last much longer than those made from other sources and offer a nearly unmatched precision in cutting other substances. Additionally, such tools work faster and much more quietly than other alternatives.
Tools made from industrial diamonds are used in the mirror and optical manufacturing fields as well as in gas and oil drilling endeavors. In the textile industry, devices made from diamonds are used to cut patterns. In medicine, cutting instruments made from diamonds are used to cleanly slice bone and tissue. The construction industry uses diamond tools in the grinding and cutting of concrete and pavement. Diamonds are also used to make needles for stereo record players.
Physical Characteristics
Diamonds are chains of carbon. Carbon is one of the most common substances on the planet. In one form it is simple graphite, used in pencils, but in its crystallized form, it takes an altogether different appearance as diamond. On the scale used by mineralogists to measure the hardness of minerals, diamonds rate ten on a scale of one to ten. Diamonds are measured in carats, the standard unit of measurement for gemstones. One carat is roughly equal to one-fifth of a gram. The carat can be further divided into points based on a scale of 100. One of the reasons diamonds are so prized is because the light they absorb is reflected directly back outward, if the stone has been properly cut. The unusual crystal structure of the gem allows this high degree of refractability. Because of their structure, diamonds are also excellent conductors of electrical current.
Structurally, the diamond can be described as an octahedron. This means that there are double four-sided pyramids of carbon chains inside that meet one another at the bases. Cubes or dodacahedrons—a twelvesided shape—are also found within the stone. Sometimes small triangular pockets called trigons can be observed.
Diamonds are found in nature in a variety of hues. Colorless or white diamonds are the most common, while some tinted stones are rare and valuable. The shades may be yellow, blue, pink, green, or amber. In South Africa it is common to see orange diamonds as jewelry, but this is a custom that has not made its way into the rest of the world. Some of the world's most famous diamonds are the colored ones—the heavy Dresden Green, for instance, and the infamous Hope Diamond. The latter, blue in color, is thought to hold certain negative energy, and many unexplained deaths have been associated with its owners. It is now in the collection of the Smithsonian Institution in Washington, DC.
Extraction and Refining
Diamonds are mined either from the kimberlite pipes below the earth's surface, or from alluvial deposits. Alluvial (riverbed) deposits occurred when volcanic action carried kimberlite and other minerals from the center of activity to naturally forming irrigation systems. Such diamonds are found quite near the earth's surface. In alluvial mining, considerable amounts of sand must first be removed from the area. The sand and other such components are called over-burden, and large mechanical scrapers are used to move it out of the way. Underneath the overburden lies a gravel bed, and bulldozers scoop the gravel up and set it aside in piles.
The piles are then taken to a screening plant, where the diamonds are extracted. In alluvial mining, it is sometimes necessary to reach the bedrock underneath the gravel bed—or sometimes even below the bedrock itself—in order to unearth the diamond deposits. The bedrock must be thoroughly searched. Sometimes an enormous vacuum device called a Vacuveyer is used for this purpose. As the mining process moves along in a horizontal fashion, the removed overburden is again deposited to fill over the excavated sites.
Below-ground mining of kimberlite for diamond also requires moving enormous quantities of rock and other material in order to unearth gems, but on a much larger scale than alluvial mining. For one part diamond uncovered, it is estimated that 15 to 30 million parts waste must be moved out of the way. Unlike mining endeavors for gold or other substances, engineers cannot determine beforehand whether an area has a large abundance of diamond.
Mining
Block caving is the most commonly used method in excavating diamonds from kimberlite deposits. This method offers the highest yield and thus is the most cost effective. First, a large vertical hole is excavated, typically 1,750 feet (533 m) in diameter. Levels are placed approximately every 40 feet (12 m). Along these levels are horizontal tunnels known as scraper drifts. In the drifts, there are small inclined coneshaped openings at intervals of every 11 feet (3 m) or so. These openings are roughly four feet by four feet. When a horizontal slice is cut above the cones—usually about six feet (1.8 m) in height—the kimberlite begins to break off and fall into the cone and into the scraper drift. The material is then pushed onto trucks. The trucks travel underground through the mining area and take the collected kimberlite to a crushing device.
Crushing
In the crushing operation, which occurs in the below-ground mining facilities, large chunks of kimberlite are broken up into more easily transportable segments. After an initial crushing, the kimberlite passes through a grizzly, or a set of iron bars. If the crushed chunks do not pass through the grizzly, they are still too large, and they are sent back for further crushing. The crushed kimberlite is then taken above the surface for further processing. When no more kimberlite is found entering the cones, the area is depleted and work moves on to a lower level.
Separating
The actual diamonds must be separated from the rock that surrounds them. Crushing or milling the excavated material is the first step, but this is done in a rudimentary form so as not to damage the potential gems inside. Next, a gravity-based device is used to sort the diamond-containing portions—called the concentrate—from the tailings, or the filler rock. One of the most commonly used methods to separate the two is a type of washing pan developed in South Africa in the 1870s. Decomposed kimberlite and water—in a mixture known as a puddle—is put into the pan. The mixture's viscosity is a crucial element, because the lighter particles will rise to the top, but the diamonds and other heavy minerals will descend to the bottom of the pan. Another method of uncovering diamonds uses media separators. A stew called a slurry is made up—typically consisting of water added to the crushed concentrate and tailings. Ferro-silicon powder, which has a heavy density, is also added.
The slurry may be put into one of three types of media separators. The first is a cone-shaped tank, with a cone-shaped agitating element inside. The agitator moves around the sides of the tank, but leaves enough room so that the lighter tailings can rise to the top and the heavier elements sink to the bottom. In a lifting-wheel type of media separator, a wheel is filled halfway with slurry. Paddles inside it agitate the mixture, and lift the heavy particles from the bottom and separate them from the rest of the mixture. The third type of media separator is known as a hydrocyclone. It is a large vat that spins around, and through centrifugal force, the heavier, diamond-rich particles are separated.
Greasing
After this rudimentary separation, the concentrate moves to a greasing area, another innovation in diamond manufacturing developed in South Africa in the late 19th century. Mixed with water, the kimberlite-and-diamond mixture is placed on a greased belt or table. This device is usually slanted and vibrated. The method operates on the premise that diamonds newly excavated will not become wet when brought into contact with water. Instead they will stick to the grease. Petroleum jelly is usually the preferred substance on the grease belt or table. The water then carries away the remaining non-diamond particles. The diamond-laden concentrate is then swept off the table and boiled to remove the traces of grease. In a newer method, X-ray technology is used to determine which of the concentrate is diamond and which is effluvial material.
Cutting
Chunks of diamond eventually become small, perfectly shaped gemstones commonly used in engagement rings and other jewelry. Since diamond is the hardest known substance, diamond dust must be used to cut the stone. In cutting, a minuscule groove is incised into the surface of the diamond, and a cleaving iron is inserted into the groove. With a quick, forceful blow, the diamond should split perfectly along its naturally occurring planes. The lapidary determines further cuts by marking them off on the surface with ink. Next, a diamond saw, oiled with the unusual combination of diamond dust and olive oil, is rotated vertically on the surface of the raw gem. This device divides the diamond into new segments. These parts are then fed into a lathe-like device for grinding.
The Future
Diamonds are a finite resource. The fate of Indian diamonds is a good example of what the future might hold for the South African diamond-mining industry. From the first discovery of the gems in India until relatively recently, it is thought that over 12 million carats originated from India. By the mid-20th century, the resources were nearly depleted, and India was producing only about 100 carats annually. Diamonds will continue to be used in industry and high-technology enterprises, but synthetically produced facsimiles—first manufactured in 1953—may accomplish some of the tasks originally the exclusive province of the real stone. These "manufactured" gems have the same properties of hardness and durability, and while they will never be as popular as the real diamond for adomment purposes, they are well suited for industrial applications.
Where To Learn More
Book
Arem, Joel A. Gems and Jewelry, 2nd ed. Geoscience Press, 1992.
Periodicals
Austin, Gordon T. "Diamond." American Ceramic Society Bulletin, May 1990, p. 854-55.
"More Australian Diamonds?" Engineering and Mining Journal, November 1992, p. 62.
"Diamond Exploration—The Trace Element Revolution." Engineering and Mining Journal, July 1994, p. 7.
Galli, Giulia, Richard M. Martin, and Roberto Car. "Melting of Diamond at High Pressure." Science, December 14, 1990, p. 1547-49.
[Sci-Tech Encyclopedia: Diamond A mineral composed entirely of carbon; the hardest substance known. Diamond is a polymorph of carbon; lonsdaleite, another polymorph, is sometimes referred to as hexagonal diamond. Diamond is found on all continents except Antarctica, which has not yet been explored for it. It occurs in nature as single crystals of gem or industrial quality, and as polycrystalline masses referred to as boart, framesite, or carbonado. It has also been found as minute black grains in some meteorites. Diamond can be synthesized in the laboratory and is produced commercially in large amounts for industrial uses. See also Carbon; Graphite.
Diamond has a cubic (isometric) crystal structure in which all carbon atoms have covalent (sp3) bonds. It is this strong bonding that makes diamond hard. Nevertheless, if diamond is struck in specific directions it will readily cleave—a property utilized in the preparation of polished gem diamonds. The combination of refractive index and dispersion gives diamond its brilliance and so-called fire when cut and polished. The thermal conductivity of diamond is the highest of any material (five times that of copper). This property, plus hardness, makes diamond an ideal material for use as a cutting tool in industry and also as a heat sink in electronics. See also Crystal structure.
Although diamond consists of carbon, at least 58 other elements have been found (for example, aluminum, 10 parts per million; hydrogen, 1000 ppm; silicon, 80 ppm) as impurities in natural diamond. However, only two, nitrogen and boron, replace carbon atoms in the diamond lattice. Nitrogen is the major impurity and may substitute for carbon in a number of ways, commonly as either isolated or paired nitrogen atoms, and as discrete platelets of nitrogen within the diamond structure. The presence or absence of nitrogen and the manner of its substitution leads to different physical properties, such as thermal conductivity, electrical restivity, and infrared spectra.
Diamond is resistant to chemical attack, other than by strong oxidizing agents. In vacuum or an inert atmosphere, a clear, colorless gem diamond transforms to a gray-black mass of graphite at about 1500°C (2700°F). In air, diamond oxidizes (burns) to carbon dioxide at and above 800°C (1500°F). At high temperature, some metals (for example, tungsten, titanium, and tantalum) react with diamond to form metal carbides. Metals, such as iron, nickel, cobalt, and platinum, in the molten state are solvents for carbon and dissolve diamond; this phenomenon is used as a basis for the synthesis of diamond.
Most natural diamond, apart from that in meteorites, crystallizes at depths of approximately 110 mi (180 km) in the Earth's upper mantle at temperatures in the range 900–1200°C (1650–2200°F). The host rock in which diamond forms is either a magnesian-rich silica-deficient ultramafic (peridotitic) rock or an ultrabasic eclogitic rock. Minerals that constitute the ultramafic type of diamond-host rock are magnesian rich and include varieties of olivine, pyroxene, and pyrope garnet. The eclogitic rock consists of sodium-bearing pyroxene and an almandine garnet. These various constituent minerals may also occur as inclusions in diamond and result in the host being identified as either an ultramafic (peridotitic) or eclogitic diamond. Diamonds in each group have formed in a distinct and different geochemical environment in the upper mantle. See also Eclogite; Lithosphere; Meteorite; Peridotite.
Diamond is eventually transported to the Earth's surface by unique types of volcanic eruption in which gases play a major role. The eruptions drill narrow (much less than 3000 ft or 1000 m) explosive vents or pipes through the crust of the Earth. Two different rock types, each containing diamond, may result and infill the volcanic neck or pipe. The first type is known as kimberlite, and the second as lamproite. The most productive mine in the world based on the number of diamonds produced per unit of host rock is based on lamproite—the Argyle mine in Western Australia. In general, diamonds are considerably older than the volcanic eruption that transported them to the surface. Thus diamonds that are 3.2 billion years old reached the surface only 85 million years ago. Diamond-dearing kimberlites occur in South Africa, Botswana, Angola, Sierra Leone, Guinea, Tanzania, Brazil, Venezuela, the United States, Canada, Russia, Siberia, China, India, and Australia. Only lamproites in Western Australia and one in Arkansas in the United States are diamond bearing.
The major production of diamond is from the primary sources in South Africa, Botswana, Zaire, Australia, and Siberia, with minor amounts coming from Tanzania and China. The diamond mines in all these countries are based on kimberlite, except for the Argyle mine in Australia, where the source rock is lamproite. Although Botswana and South Africa produce the most gem diamonds, as well as Russia whose production is difficult to assess, the major worldwide production is from the Argyle mine in Australia, albeit mostly industrial diamonds. Diamond production from secondary (alluvial or placer) deposits, apart from the extensive mining of the marine gravels off the west coast of southern Africa, is relatively small compared to the output from mines based on kimberlite and lamproite. Alluvial deposits in Guinea, Ghana, Russia, and Australia are mined by large companies or government agencies. All other alluvial diamond deposits are worked by small local groups or individual miners. See also Placer mining.
Rough diamonds occur in a variety of shapes, including octahedra, dodecahedra, twinned octahedra (macle), and broken or cleavage fragments. The largest diamond found, the Cullinan, was a cleavage fragment. After the rough is sorted into cuttable (gem and near gem) and industrial stones, the decision is made as to how a specific diamond will be shaped and made into a polished gem. The cutting and polishing process can result in the loss of as much as 60% of the original diamond.
Polished diamonds are graded on the basis of the 4 C's—carat, cut, clarity, and color. The carat is the unit of weight in the diamond industry and is standardized as 0.2 gram (0.0071 oz or 200 milligrams) and is divided into 100 points. Thus a 10-point diamond weighs 0.1 ct (0.00071 oz or 20 mg). The largest diamond, the Cullinan, weighed about 3000 ct (4.27 oz or 600 g) and was the size of an average human fist. The grading cut is based on how well the facets and the shape of a polished diamond compare to a standard model. See also Gem.
Diamonds, although commonly considered to be mostly colorless, actually exist in all the colors of the rainbow. Colored stones are known as fancies, and if of excellent uniform color they are most desirable.
Diamonds were first synthesized in Sweden in 1953. These early experiments used the principle that carbon dissolves in the transition elements of groups 8–10 (such as iron or nickel). At high pressures (50–60 kilobars or 5–6 gigapascals) and temperatures (1500°C or 2700°F), the dissolved carbon nucleates and crystallizes as diamond. Direct conversion of graphite to diamond was achieved in 1961 in shock-wave experiments in which transient high pressures in excess of 300 kb (30 GPa) and temperatures of about 1100°C (2000°F) existed.
Synthetic diamonds generally are not large; most are produced in sizes below 0.004 in. (0.1 mm). These are used extensively as grit for industrial grinding purposes. Colorless gem-quality diamond can also be synthesized, but the cost of synthesis has proved to be greater than the cost of the natural product.
Diamond films can be grown in several ways. For example, diamond crystals up to 0.02 in. (0.5 mm) in size can be formed from a mixture of methane and hydrogen at about 50 torr (6.7 kPa) pressure and 1000°C (1900°F) on a silicon substrate. This method is known as thermally induced chemical vapor deposition, but other techniques may be used, including plasma chemical vapor ion depostion and electron-beam deposition. The diamond films display properties similar to those of natural diamond and have similar hardness and thermal conductivity, both significant properties for the uses of diamond films. See also Vapor deposition.
Diamond, apart from its use as a gem, has numerous applications in industry, and it is designated a strategic mineral. Many of the uses of natural and synthetic diamond are equivalent. Originally, natural diamond, including boart, carbonado, and framesite, was crushed to various sizes of powder and used as grinding and polishing agents for glasses, ceramics, and nonferrous metals. Diamonds, as single crystals or powders, are also bonded in metal drills and bits. Small drills are used in applications such as dental work; large drills are used in drilling for oil and other minerals. Diamond-impregnated wheels are used for cutting many hard materials, including concrete and dimension stone for architectural purposes. Synthetic diamond is sometimes preferred for various uses, as it is grown to the specific grain size rather than crushed as in the case of natural diamond. Diamonds are used in eye surgery, and also as heat sinks and semiconductors in the electronics industry. Diamond films have potential uses as scratchproof coatings on optical lenses, compact discs, and even on nondiamond jewelry; bearings in machines; heat sinks and semiconductors in electronics; and general inert coatings or surfaces in areas of high chemical corrosion. Natural diamond has also been used as optical windows in spacecraft.
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Investment Dictionary: Diamonds 1. An extremely hard gemstone used mainly for jewelry, tools and as an investment in precious stones.
2. The informal term for an index-based unit investment trust, known formally as Diamonds Trust Series 1.
Investopedia Says:
2. The Diamonds Trust Series 1 trades on the American Stock Exchange under the ticker symbol "DIA". It is commonly referred to as an exchange-traded fund (ETF) by the investing public and the financial media; however, this is not entirely accurate. A share of DIA provides an investor with a fractional ownership in the 30 stocks represented in the Dow Jones Industrial Average (DJIA) index.
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Financial & Investment Dictionary: Diamonds Units of beneficial interest in the Diamonds Trust, a Unit Investment Trust that holds the 30 component stocks of the Dow Jones Industrial Average. First introduced in January, 1998, Diamonds trade under the ticker symbol "DIA" like any other stock on the American Stock Exchange. They are designed to offer investors a low-cost means of tracking the Dow Jones Industrial Average, the most widely recognized indicator of the American stock market. Diamonds pay monthly Dividends (which can be reinvested into more shares of the trust) that correspond to the dividend yields of the component stocks of the Dow and pay capital gains distributions once a year. Diamonds are designed to trade at about 1/100 the level of the Dow Jones Industrial Average, so if the parent group comprises the Madrid, Barcelona, Bilbao, and Valencia stock exchanges, MF Mercados Financieros, Iberclear, and BME Consulting, low is at 10000, Diamonds will trade at about $100 per unit. Unlike open-end mutual funds, Diamonds trade like stocks, allowing investors to buy or sell at any time during the trading day, whereas index mutual funds are priced only once at the end of each trading day. Like open-end index funds, Diamonds charge low-management fees because there is little research or trading conducted by the trust's management. There are also no Loads to buy Diamonds, though normal brokerage commissions do apply to trades. Whereas closed-end funds often trade at discounts to their Net Asset Values, investors can create an unlimited number of Diamonds trading units, which helps insure they will correlate closely with the performance of the Dow stocks in the portfolio. See also Index Fund; Spdr; Exchange-Traded Funds (ETFS). www.amex.com/dia.
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Dental Dictionary: diamond
n A crystalline carbon substance, the hardest natural substance known, used industrially and in dentistry for cutting and grinding.
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Britannica Concise Encyclopedia: diamond .content{clear:both;}
Mineral composed of pure carbon, the hardest naturally occurring substance known and a valuable gemstone. Diamonds are formed deep in the Earth by tremendous pressures and temperatures over long periods of time. In the crystal structure of diamond, each carbon atom is linked to four other, equidistant, carbon atoms. This tight crystal structure results in properties that are very different from those of graphite, the other common form of pure carbon. Diamonds vary from colourless to black and may be transparent, translucent, or opaque. Most gem diamonds are transparent and colourless or nearly so. Colourless or pale blue stones are most valued, but most gem diamonds are tinged with yellow. Because of their extreme hardness, diamonds have important industrial applications. Most industrial diamonds are gray or brown and are translucent or opaque. In the symbolism of gemstones, the diamond represents steadfast love and is the birthstone for April. For more information on diamond, visit Britannica.com.
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Columbia Encyclopedia: diamond, mineral, one of two crystalline forms of the element carbon (see allotropy), the hardest natural substance known, used as a gem and in industry. Properties
Diamonds crystallize in the isometric system (see crystal) commonly as transparent to translucent white, colorless, yellow, green, blue, or brown octahedrons (the familiar diamond shape). The extraordinary brilliancy of diamonds after faceting is due to their very high refractive index, which is greater than that of any other naturally occurring gemstone. In addition to the gem varieties there are bort, which is poorly crystallized or of inferior color and in fragmentary condition, and carbonado (black diamond), which is gray to black and opaque, with poor cleavage. Bort and carbonado are used as abrasives, in the cutting of diamonds, and for the cutting heads of rock drills. Diamond abrasives may have been used as early as 2500 B.C. in China.
Natural Occurrence and Processing
Diamonds are found in alluvial (loose earthy material deposited by running water) formations and in volcanic pipes, filled for most of their length with blue ground or kimberlite, an igneous rock consisting largely of serpentine. At the surface the blue ground is weathered to a clay called yellow ground. Diamantiferous (or diamondiferous), or diamond-yielding, earth is mined both by the open-pit method and by underground mining. After being removed to the surface, it is crushed and then concentrated. Sorting is done by passing the concentrated material in a stream of water over greased tables. The diamond, being largely water repellent, sticks to the grease, but the other minerals retain a film of water, which prevents them from adhering to the grease. The diamonds are then removed from the grease, cleaned, and graded for sale.
Sources
The earliest sources of gem diamonds were India and Borneo, where they were found in river alluvium. All famous diamonds of antiquity were Indian diamonds, including the Great Mogul, the Orlov, the Koh-i-noor, and the Regent or Pitt. Other famous diamonds are the Hope (blue), Dresden (green), and Tiffany (yellow). In the early 18th cent., deposits similar to those in India were found in Brazil, mainly of carbonados, though they may have been known as early as 1670. In 1867, a stone found in South Africa was recognized as a diamond. Within a few years, this began a wild search for diamonds, both in river diggings and inland. In 1870–71, dry diggings, including most of the celebrated mines, were discovered. Well-known South African diamond mines are the Dutoitspan, Bultfontein, De Beers, Kimberley, Jagersfontein, and Premier. Botswana, Namibia, Cananda, and South Africa are now the world's major diamond-producing nations; other important countries include Australia, Russia, Brazil, Angola, Sierra Leone, Ghana, Tanzania, and Venezuela. The use of diamonds to finance African rebel groups and fuel civil strife in the 1990s led, in 2001 and 2002, to international agreements (the Kimberly Process) designed to certify legitimately mined diamonds, but so-called blood diamonds remain a source of financing for the conflict in Côte d'Ivoire.
Synthetic diamonds were successfully produced in 1955; a number of small crystals were manufactured when pure graphite mixed with a catalyst was subjected to pressure of about 1 million lb per sq in. and temperature of the order of 5,000°F (3,000°C). Synthetic diamonds are now extensively used in industry.
The Diamond Cartel
The discoveries of 1870–71 in South Africa led to a great number of prospectors staking out claims and securing the diamonds by open-pit or quarry mining. The damage caused by floods and mudslides, unavoidable when there were so many different claims, was an important factor in the series of amalgamations carried on by Cecil Rhodes and Barnett Barnato. Rhodes brought about the merging of their interests in the De Beers Consolidated Mines, Ltd., which established (1889) an effective monopoly over the diamond industry. Loss of diamonds by theft was reduced through the passage of the so-called I.D.B. (Illicit Diamond Buying) Act, which limited the trade to licensed buyers and imposed penalties for the possession of uncut stones without a license. Thefts were further curtailed by the institution of compounds in which the workers live while employed by the company and which they leave only after being thoroughly searched.
Most of the major diamond producers belong to, or have cooperated with, the De Beers–led marketing cartel, formed to maintain the price of diamonds at a high level. De Beers, under Harry Oppenheimer's leadership (1957–84), maintained its dominant position in the industry by using its numerous worldwide companies to buy up new sources of diamonds and to control distribution of industrial diamonds and production of synthetic ones. In the last decades of the 20th cent., however, De Beers' hold over the unpolished diamond market decreased, and in 2000 the company announced it would end to its policy of controlling diamond prices through hoarding and shift its focus to increasing sales.
Bibliography
See V. Argenzio, Diamonds Eternal (1974); A. N. Wilson, Diamonds: From Birth to Eternity (1982); R. Newman, Diamonds: Fascinating Facts (1990); S. Kanfer, The Last Empire (1993).
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Occultism & Parapsychology Encyclopedia: Diamond This gem was believed to possess the most marvelous virtues. It gave victory to whomever carried it on his left arm, whatever the number of his enemies. Panics, pestilences, enchantments were all said to fly before it; hence, it was good for sleepwalkers and for the insane. It deprived the lodestone of its virtue, and one variety, the Arabian diamond, was said to attract iron more powerfully than a magnet.
The diamond is the hardest substance known, a property referring to its resistance to being scratched, rather than its resistance to other forces, such as the strike of a hammer. Ancient peoples believed that neither fire nor blows would overcome its hardness, unless the diamond was macerated with fresh goat's blood. Cyprian, Austin, Isidore, and other church fathers, adopting this notion, used it to illustrate the method by which the blood of the Cross softens the heart of man.
If bound to a magnet, the diamond, according to the belief of the ancients, would deprive it of its magnetic property.
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Rock & Mineral Guide: diamond
C
Cubic -- hextetrahedral Environment Formed at great depths in subcrustal iron-magnesium magmas, and ferried to the surface in volcanic lavas. Thanks to their toughness and density, now commonly residual in alluvial deposits derived from the disintegration of dark plutonic rocks.
Crystal description Most often in brilliant, commonly well-formed, triangularly pitted octahedrons. The cube faces are never smooth; though the crystal is unmistakably dicelike, its faces are always uneven but still lustrous. Smooth and shiny hexoctahedrons are usually almost spherical, marked by curved faces. Also in translucent balls with a radiating structure, known as "ball bort" or ballas, and in irregular hard black compact masses known as carbonado. Flat triangular crystals are usually spinel-twinned octahedrons known in the diamond trade as "macles."
Physical properties White, or tinted all hues, gray to black. Luster adamantine; hardness 10; specific gravity 3.52; fracture conchoidal; cleavage perfect octahedral, poor dodecahedral; brittle; often fluorescent and phosphorescent; blue stones often electrically conducting.
Composition Carbon; a little nitrogen makes for yellower crystals.
Tests Infusible, insoluble. Burns at high temperatures (about 500°C). At slightly lower temperatures the surface frosts (can be repolished, if disaster strikes).
Distinguishing characteristics The submetallic (adamantine) luster is unmistakable when combined with the crystal form and hardness. The quartz pebbles with which diamond is most often confused by hopeful dreamers (because quartz too will scratch glass) are wholly different in luster and fly apart with heat.
Occurrence In alluvial deposits the harder and heavier diamonds survive when parent rock weathers and is worn away. They are mined from the original rocks only in Siberia, South Africa, Australia, and in Arkansas. They usually occur in a basic plutonic rock in cylindrical, more or less vertical, volcanic plugs known as "pipes." In Canada many suitably located pipes (and glacial deposit finds) indicate that there is a possibility of economic diamond-bearing formations in the north. Alluvial localities, perhaps reweathered with their prime source long gone, are numerous. Sporadic diamonds are found in gold placers in the eastern U.S. and in California. In recent decades Siberia has become an important source. Brazil, New Guinea, India, Namibia, and other African states have many localities, though none has proved notably large or abundant.
Remarks Though promotions claim that only about 20 percent of the diamonds found are suitable for gem use, in fact the percentage is far higher, with Indians proving adept at obtaining small stones from what was long considered hopeless bort (poor-quality diamond material). Industrial diamonds are used for tools and dies, with the lowest grades crushed to a fine abrasive powder. The difference in hardness between diamond (10) and corundum (9) is said to be great, with diamonds almost twice as hard as their nearest Mohs neighbor. Synthetic diamonds are now an enormous business, but as of 1996, it is not believed that gem material production is economically practical. Cuttable crystals have been grown, but their cost is great, and their hue not of gem quality.
Irradiation (cyclotron, nuclear reactor pile, or electrons) produces greenish hues; heat then changes the greenish to yellow, golden, or chestnut. Long treatment makes them black. Zircon blues come from electron treatment followed by light heating. Fancier hues are unpredictable and usually minute.
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