How Diamonds Work

By: Kevin Bonsor
The Hooker Diamond necklace, earrings and ring on display at the National Museum of Natural History. See more diamond pictures.
Photo courtesy Smithsonian Institution/Chip Clark

On your next trip to the local shopping mall, stop by one of the jewelry stores. Notice the diamond jewelry that takes up the majority of the showcase and the number of people hovering over the counters trying to pick out diamonds for their loved ones. There will surely be a salesperson explaining the "4 Cs" -- cut, clarity, carat and color -- to a young shopper, and explaining why one diamond is better than the one right next to it. Why all the fuss over diamonds?

A diamond is just carbon in its most concentrated form. That's it -- carbon, the element that makes up 18 percent of the weight of your body. In many countries, including the United States and Japan, there is no other gemstone as cherished as the diamond, but in truth, diamonds are no rarer than many other precious gems. They continue to demand higher market prices because the majority of the diamond market is controlled by a single entity.


In this article, we will track a diamond from the time it is formed to when it reaches the Earth's surface. We will also examine the artificial rarity created by the diamond cartel, De Beers, and briefly discuss the properties of these gems.

First, we'll discuss carbon, the element behind the sparkle.


Carbon and Kimberlite

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Carbon is one of the most common elements in the world and is one of the four essentials for the existence of life. Humans are more than 18 percent carbon. The air we breathe contains traces of carbon. When occurring in nature, carbon exists in three basic forms:

  • Diamond - an extremely hard, clear crystal
  • Graphite - A soft, black mineral made of pure carbon. The molecular structure is not as compact as diamond's, which makes it weaker than diamond.
  • Fullerite - A mineral made of perfectly spherical molecules consisting of exactly 60 carbon atoms. This allotrope was discovered in 1990.

Diamonds form about 100 miles (161 km) below the Earth's surface, in the molten rock of the Earth's mantle, which provides the right amounts of pressure and heat to transform carbon into diamond. In order for a diamond to be created, carbon must be placed under at least 435,113 pounds per square inch (psi or 30 kilobars) of pressure at a temperature of at least 752 degrees Fahrenheit (400 Celsius). If conditions drop below either of these two points, graphite will be created. At depths of 93 miles (150 km) or more, pressure builds to about 725,189 psi (50 kilobars) and heat can exceed 2,192 F (1,200 C). Most diamonds that we see today were formed millions (if not billions) of years ago. Powerful magma eruptions brought the diamonds to the surface, creating kimberlite pipes.


Kimberlite is named after Kimberley, South Africa, where these pipes were first found. Most of these eruptions occurred between 1,100 million and 20 million­ years ago.


Kim­berlite pipes are created as magma flows through deep fractures in the Earth. The magma inside the kimberlite pipes acts like an elevator, pushing the diamonds and other rocks and minerals through the mantle and crust in just a few hours. These eruptions were short, but many times more powerful than volcanic eruptions that happen today. The magma in these eruptions originated at depths three times deeper than the magma source for volcanoes like Mount St. Helens, according to the American Museum of Natural History.

The magma eventually cooled inside these kimberlite pipes, leaving behind conical veins of kimberlite rock that contain diamonds. Kimberlite is a bluish rock that diamond miners look for when seeking out new diamond deposits. The surface area of diamond-bearing kimberlite pipes ranges from 2 to 146 hectares (5 to 361 acres).

Diamonds may also be found in river beds, which are called alluvial diamond sites. These are diamonds that originate in kimberlite pipes, but get moved by geological activity. Glaciers and water can also move diamonds thousands of miles from their original location. Today, most diamonds are found in Australia, Borneo, Brazil, Russia and several African countries, including South Africa and Zaire.

In the next section, we'll learn why the properties of diamond make it such a unique gem.

The Properties of Diamonds

These rough stones will become dazzling diamonds after they are cut and polished.
Getty Images

Diamonds are found as rough stones and must be processed to create a sparkling gem that is ready for purchase.

As mentioned before, diamonds are the crystallized form of carbon created under extreme heat and pressure. It's this same process that makes diamonds the hardest mineral we know of. A diamond ranks a 10 on the Mohs Hardness Scale. The Mohs Scale is used to determine the hardness of solids, especially minerals. It is named after the German mineralogist Friedrich Mohs. Here's the scale, from softest to hardest:


  1. Talc - easily scratched by the fingernail
  2. Gypsum - just scratched by the fingernail
  3. Calcite - scratches and is scratched by a copper coin
  4. Fluorite - not scratched by a copper coin and does not scratch glass
  5. Apatite - just scratches glass and is easily scratched by a knife
  6. Orthoclase - easily scratches glass and is just scratched by a file
  7. Quartz - (amethyst, citrine, tiger's-eye, aventurine) not scratched by a file
  8. Topaz - scratched only by corundum and diamond
  9. Corundum - (sapphires and rubies) scratched only by a diamond
  10. Diamond - scratched only by another diamond

Researchers had determined diamonds from a crater in Arizona were formed by a meteorite. In addition to its size and heat, the meteorite had one other significant component: metal. GE scientists reasoned that they could make diamonds using a smaller-scale meteorite crash in a laboratory. They combined carbon atoms with the liquid metal troilite and added heat and pressure. The result? A crystallization of diamonds. To learn more about the experiment, read NOVA's transcript of "The Diamond Deception [source: NOVA].

Even though diamond is only one level higher on the scale than corundum, diamond can be anywhere from 10 to hundreds of times harder than this class of gems.

It is the molecular structure of diamonds that makes them so hard. Diamonds are made of carbon atoms linked together in a lattice structure. Each carbon atom shares electrons with four other carbon atoms, forming a tetrahedral unit. This tetrahedral bonding of five carbon atoms forms an incredibly strong molecule. Graphite, another form of carbon, isn't as strong as diamond because the carbon atoms in graphite link together in rings, where each atom is only linked to one other atom.

Cutting Diamonds


Th­ere are special techniques that are used to cut and shape a diamond before it gets to the jewelry store. Diamond cutters use these four basic techniques:

  1. Cleaving - To cut a rough diamond down to a manageable size, the cutter must cleave it along the diamond's tetrahedral plane, where it is the weakest. A wax or cement mold holds the diamond in place while the cutter carves a sharp groove along the plane. The cutter places a steel blade in the groove and forcefully strikes it, cutting the rough diamond in two.
  1. Sawing - Sometimes, diamonds have to be cut where there is no plane of weakness, which cannot be done with cleaving. Instead, the cutter saws the diamond using a phosphor-bronze blade rotating at about 15,000 rpm. Lasers can also be used to saw diamonds, but the process takes hours. During the sawing step, the cutter decides which parts of the diamond will become the table (the flat top of the stone with the greatest surface area) and the girdle (the outside rim of the diamond at the point of largest diameter). Then, he proceeds to cutting.­
  2. Bruiting/Cutting - This technique gives diamonds their shape. When diamonds are cut by hand, the technique is called bruiting -- cutting refers to bruiting by machine. When the cutter shapes diamonds by hand, he relies on the diamond's hardness as his tool -- he uses diamonds to cut diamonds. He uses a small, stick-like instrument with a cement-filled bowl at the tip to hold the diamond. The diamond is inserted in cement with just one corner exposed. Using one of these sticks in each hand, the cutter rubs the exposed diamond parts together to bruit them. In the mechanical process, the diamond is placed in a lathe, and another diamond in the lathe rubs against it to create the rough finish of the g­irdle.
  1. Poli­shing - To create the diamond's finished look, the cutter places it onto the arm above a rotating polishing wheel. The wheel is coated with an abrasive diamond powder that smoothes the diamond as it is pressed against the wheel.

Next, we'll learn what determines the beauty and worth of a diamond.


The Four Cs

Diamonds are judged on several factors that determine their beauty. Most diamonds never reach the consumer market because they are too flawed. Often, these diamonds are used for industrial purposes -- as an abrasive, for drill bits or for cutting diamonds and other gems. If you've ever purchased a diamond, you've heard of the "4 Cs:"

  1. Cut - This refers to a diamond's geometric proportions and how it has been cut. When a diamond is cut, facets are created and the diamond's finished shape is determined.
  2. Clarity - This is the measurement of a diamond's flaws, or inclusions that are seen in the diamond. Clarity levels begin with Flawless and move down to Very Very Slight (VVS), Very Slight (VS) and Slightly Included (SI).
  3. Carat - This is the weight of a diamond. One carat is equal to about 200 milligrams.
  4. Color - In referring to transparent diamonds, the color scale runs from D to Z, beginning with Icy White -- the color of the most expensive transparent diamonds -- and ending with a light yellow.

Other unique qualities of the diamond include its transparency, luster and dispersion of light. A diamond that is created from 100-percent carbon will be completely transparent. Diamonds often contain other elements that can affect their color. Although we often think of diamonds as being clear, there are also blue, red, black, pale green, pink and violet diamonds. These natural colored diamonds are the truly rare ones, and thereby can sometimes be the most costly.


Photo courtesy Getty Images Only the very best diamonds will be mounted into extravagant bracelets, earrings and rings like these.

Diamonds are made in the molten magma deep inside the Earth. Only nature can create diamonds, but it is people who have created the artificial rarity that has spurred demand for these gems. Carbon is one of the most common elements in the world, and diamonds are a form of carbon. Naturally occurring diamonds are no more rare than many other precious gems. The truly rare transparent diamonds are those rated as flawless, meaning that they don't have the slightest imperfection.

Diamonds were not always so popular with the American public, and they were not always so pricey. A diamond placed in a mounting on a ring has a markup of about 100 percent to 200 percent. The only reason why we pay so much more for diamonds today than for other precious gems is because the diamond market is controlled almost entirely by a single diamond cartel, called De Beers Consolidated Mines, Ltd., which is based in South Africa.

De Beers stockpiles diamonds mined from countries around the world and releases a limited number of diamonds for sale each year. De Beers produces half of the world's diamond supply and controls about two-thirds of the entire world market, according to a Washington Post report. At times, just to keep prices up, De Beers has bought tremendous numbers of diamonds from countries attempting to inject large quantities into the market. If De Beers were a U.S.-based company, it would be in violation of antitrust laws for fixing the prices of diamonds.

Next, we'll learn about the marketing strategies behind De Beers' success.

Marketing Diamonds

The secret to De Beers' success is a marketing campaign that has permeated our culture --­convincing every woman that she should r­eceive a diamond ring from her fiancé and c­onvincing each groom-to-be to pay "two-months salary" for that ring to show how much his love is worth.

Prior to the 1930s, diamond rings were rarely given as engagement rings. Opals, rubies, sapphires and turquoise were deemed much more exotic gems to give as tokens of one's love, according to the book "Twenty Ads that Shook the World" by James B. Twitchell. Twitchell goes on to describe how De Beers changed the world diamond market.


This idea of connecting diamonds to romance was captured in a brilliant ad campaign begun in the 1940s, causing demand for diamonds to increase. Surely you've heard the De Beers advertisement that "A Diamond is Forever." This ad campaign, which was created by the N.W. Ayer advertising agency in 1947, transformed the diamond market. In 2000, Advertising Age magazine named the ad campaign the slogan of the 20th century. De Beers infiltrated Japan with the same ad campaign in the 1960s, and the Japanese public bought into the idea as much as the Americans did.

Later ads by De Beers told consumers to hold onto their family's diamond jewelry and to cherish it as heirlooms -- and it worked. This eliminated the aftermarket for diamonds, which further enabled De Beers to control the market. Without people selling their diamonds back to jewelers or to other people, the demand for new diamonds increased.

There are fewer than 200 people or companies authorized to buy rough diamonds from De Beers. These people are called sightholders, and they purchase the diamonds through the Central Selling Organization (CSO), a subsidiary of De Beers that markets about 70 percent to 80 percent of the world's diamonds. De Beers sells a parcel of rough diamonds to a sightholder, who in turn sends the diamonds to cutting facilities and then to distributors.

Some rough diamonds are sold outside the CSO. These diamonds come from small producers in Australia, Russia and some African countries. The cost of these diamonds is still largely influenced by the prices set by the CSO.

Diamonds are the most coveted of all precious gems, as is witnessed by the extremely high demand for them. While this has not always been the case, diamonds are nonetheless exquisite gems that go through a long, tedious refining process from the time they are pulled from the ground to when you see them in the jewelry store. And, while some of the mystique of diamonds may be gone -- they're just carbon, after all, the diamond will likely continue to be a highly coveted jewel, because, well, "A Diamond is Forever."

But, as the saying goes, beauty often comes at a price. And, sometimes, that price goes beyond the financial realm. In the next section, we'll examine some of the biggest controversies in the diamond industry.

Diamond Controversy

Indian children cut diamonds that are too small for adults' eyes and fingers.
Photo courtesy Getty Images

If you've ever shopped for a diamond, you know that weighing the 4 Cs is hard enough without having to think about the diamond trade. But ethically speaking, a diamond's origins can be your most important consideration. Perhaps the biggest controversy facing the diamond trade today is conflict diamonds. These stones are also known as blood diamonds because of the blood shed to obtain them.

A conflict diamond has been stolen or illegally mined and then sold to raise money for rebel militia or terrorist groups. These groups earn money for weapons by forcing men, women and children to dig for diamonds. Anyone who protests is killed or threatened by having a limb cut off. Most conflict diamonds come from Angola, the Democratic Republic of the Congo, the Ivory Coast, Liberia and Sierra Leone. If you don't shop carefully, you could be buying one of these stones.


Conflict diamonds are smuggled into the diamond trade along with legitimate diamonds. The United Nations (UN), the Conflict Free Diamond Council and other groups are working toward better regulation so that conflict diamonds don't make it to the market. These groups have instituted the Kimberley Process, which monitors and certifies a diamond at every point of its production process. Because of the Kimberley Process, the UN estimates that 99.8 percent of diamonds on the market now are conflict-free [source: National Geographic]. Before you purchase a diamond, you can request to see its conflict-free certificate -- in the future, the UN will also require diamonds to have laser engraving and optical signatures, and to be entirely produced within a single country.

Conflict diamonds are not the only controversy darkening the diamond trade: human- and animal-rights issues run rampant in India as well as certain countries in Africa. In some African countries, miners use children to dig in tight, underground spaces where men and woman can't fit, even though child labor is illegal. The mining towns in these African countries also have steadily increasing murder and HIV infection rates as a result of trespassing and sex trade. In India, where 92 percent of the world's smaller diamonds are cut, children are given the smallest stones to work with because their eyes and fingers are better suited for seeing and shaping tiny facets [source: MSN]. Severe eyestrain, repetitive motion injuries and lung infections from inhaling diamond dust are just a few conditions that affect these workers.

Animal-rights activists have just as much at stake in diamond industry regulation as human-rights organizations. According to the Animal Welfare Institute, African primate populations are dwindling -- in 15 to 20 years, apes will become extinct. The chimpanzee population has declined to only 150,000, and with 600 gorillas being poached yearly, they're facing extinction as well. The dwindling primate population may be partly attributed to poaching, but not all poaching is for s­port. Some hungry diamond miners with no other food source depend on these animals for survival.

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Next, we'll delve into diamond history to learn about the discovery of some truly extraordinary diamonds.

Famous Diamonds

Cullinan II, the Lesser Star of Africa, was cut into many smaller diamonds that are in the Imperial State Crown.
Photo Courtesy Getty Images


The world's most famous diamonds are its largest diamonds. At staggering weights up to thousands of carats, these diamonds have been cut, re-shaped and sold many times, contributing to their rich, interesting histories. Despite diamond's natural, clear brilliance, some of these stones have a dark side.


  • The Cullinan - This 3,106-carat diamond is the largest diamond ever found. It was discovered in 1905 in Transvaal, South Africa. In 1907, the diamond was presented to King Edward VII of England. Later, it was cut into nine major stones, including the 530.20-carat Star of Africa diamond that is set in the Royal Scepter displayed in the Tower of London.
  • The Hope Diamond - Possibly the most famous diamond in America, this 45.52-carat diamond is on display at the National Museum of Natural History in Washington D.C. Its history dates back to the 1600s, when it was originally a 112.1875-carat diamond. In 1668, it was purchased by King Louis XIV, of France. It is believed to have been originally found in the Kollur mine in Golconda, India. The diamond was recut in 1673, creating a smaller 67.125-carat stone. You can learn more about the Hope Diamond at the Smithsonian.
  • The Excelsior - Perhaps the second-largest diamond ever found, the Excelsior was found in 1893 in South Africa. The original stone weighed about 995 carats. In 1904, I.J. Asscher and Company of Amsterdam cut the Excelsior into 21 polished stones weighing between 1 and 70 carat­s.
  • The Great Mogul - Believed to be the third-largest uncut diamond ever found, it was discovered around 1650. Its original size is said to have been 787.50 carats, but it was cut to just 280 carats. The diamond is named for Shah Jehan, who built the Taj Mahal. After the diamond was cut, he fired the cutter for doing such a poor job. Mysteriously, the whereabouts of the Great Mogul diamond are unknown today.

Most people can only dream of owning a diamond as large as these famous stones -- but synthetic diamonds could change that. In the next section, we'll learn about different synthetic diamonds.

Synthetic Diamonds

Photo ­courtesy Carnegie Institute of Washington Orange and yellow synthetic diamonds like these are less expensive than colored natural diamonds, which are rare.

For people who can't afford real diamonds or want a 100-percent guarantee that their diamond is conflict-free, synthetic diamonds are a good substitute. For many years, the only synthetic option available was cubic zirconia, but now consumers can also choose from Moissanite and man-made diamonds.

Cubic zirconia, commonly called CZ, is a laboratory gem that has been on the market since 1976. It's a hard gem (8.5 on the Mohs Scale), but it's not as hard as diamond. On the one hand, CZ is compositionally superior to diamond. CZ has greater brilliance and sparkle, it's entirely colorless and it has no inclusions. However, most consumers agree that CZ is simply too perfect -- it looks artificial even to the naked eye. Because of this, some CZ manufacturers have started producing the gem with colored tints and inclusions so that it more closely resembles diamond.


Moissanite has become CZ's biggest synthetic rival. Moissanite became available in 1998, and it's even more similar to diamond in composition and appearance. Moissanite is harder than CZ, but at 9.5 on the Mohs Scale, it is still softer than diamond. Moissanite's color is faintly yellow or green, and the tint becomes more apparent in larger stones. It also has small, stretch-mark-like inclusions that form during its growing process. Like CZ, Moissanite is more radiant than diamond, but this quality is considered a disadvantage rather than an advantage.

Photo courtesy LifeGem A LifeGem like this yellow dia­mond commemorates a deceased loved one.

­ The closest synthetic approximation to diamond is a man-made diamond. Unlike CZ and Moissanite, man-made diamonds are pure carbon. The Gemological Institute of America (GIA) recognizes these as real diamonds from a compositional perspective. But, the man-made diamonds don't have the rich geological history that natural diamonds do. Laboratories simulate the heat and pressure from the Earth's mantle that create natural diamonds. For the synthetic manufacturers and the consumers, diamonds come down to a matter of time and money: days versus millions of years, thousands of dollars versus tens of thousands of dollars or more (man-made diamonds sell for about 30 percent less than natural ones) [source: MSN]. If you want a uniquely colored, relatively inexpensive diamond (it will cost less than a natural colored diamond), you can find man-made ones in shades of orange, yellow, pink and blue. Finding a large diamond will prove a greater challenge -- most man-made diamonds weigh less than one carat. If you want the best synthetic has to offer, man-made diamonds are a no-brainer. Even jewelers can have a hard time telling them apart from natural ones. To prevent retailers from passing off man-made diamonds as natural ones, the GIA is selling machines that will help jewelers easily distinguish between the two.

It may come as no surprise that the developer behind these machines is none other than the king of the natural diamond industry: De Beers.

For more information on diamonds and related topics, check out the links on the next page. ­

Lots More Information

Related HowStuffWorks Articles

More Great Links


  • "The Art of Cutting Diamonds: The Manner of Preparing the Gems for the Market." The New York Times. 9/7/1885 (10/9/2007). 9F05E3DD1139E533A25754C0A96E9C94649FD7CF
  • "Blood Diamonds- Conflict Diamonds- What is the Kimberley Process?" (10/9/2007)
  • "Bushmeat." The Animal Welfare Institute. (10/9/2007). othercampaigns/Bushmeat/bushmeat.pdf+Bushmeat+the+taste +of+extinction&hl=en&ct=clnk&cd=2&gl=us
  • "Conflict Diamonds." United Nations Department of Public Information. 3/21/2001. (10/9/2007).
  • "Cubic Zirconia." Estate Antique Jewelry Sarasota Gold and Silver. (10/9/2007).
  • Hussain, Sakina Sadat and Peter Cahill. "A Diamond's Journey." (10/10/2007).
  • JJKent, Inc. "About the Early Methods of Cleaving, Sawing, and Cutting Diamonds." 2004 (10/9/2007). diamonds.htm
  • LifeGem. "LifeGem. More than a Breakthrough." 2006 (10/9/2007)
  • "Moissanite." Diamonds are Forever Index. (10/9/2007).
  • Mulrean, Jennifer. "Man-made diamonds: a girl's new best friend?" MSN Money. (10/9/2007).
  • NOVA. "The Diamond Deception." 2/1/2000 (10/15/2007) NOVA Transcripts: PBS.
  • Roach, John. " 'Blood Diamonds' and How to Avoid Buying Illicit Gems." National Geographic News. 12/8/2006 (10/9/2007).