Diamond

On the nature of diamond

That most precious of gems, the diamond, is created under extremely high temperatures and pressure that only exist 100 miles beneath the earth’s surface. Imagine how many diamonds must be sleeping deep beneath the surface of our planet.  We find and mine the ones that have been ejected violently upwards and are much "easier" to collect.

Diamond crystal in kimberlite. Image from the Smithsonian Institution.

Diamond crystal in kimberlite. Image from the Smithsonian Institution.

Diamond is the only gemstone composed of a single element: carbon.  In fact, diamonds are typically about 99.95 percent carbon. The remaining 0.05 percent bit can include one or more trace elements, which don't have an impact on the diamond’s essential chemistry, although sometimes these trace elements can influence color or crystal shape.

On finding diamond and what to look for

Diamonds are mined in many places on our amazing planet, but primarily in Africa. However, you never know when or where the next big discovery will occur. For example, after many years of searching, diamond deposits were found by geologists in remote Canada -- and the Ekati mine, composed of six open pits, was put into production in the late 1990s.

The pits at Ekati diamond mine.

The pits at Ekati diamond mine.

The history of diamonds begins in India where diamonds were gathered from rivers and streams. Some historians believe that India was trading in diamonds as early as the fourth century BC. For many centuries India was the primary, if not the only, source of diamonds to civilized cultures, including Ancient Rome.  With time, India's diamond deposits were depleted and their operations are now quite small in scale.

These days when we think of diamonds, we think of Africa.  Many countries in Africa have substantial diamond industries.  Botswana is a major sources of contemporary diamonds but other countries include the Congo and Sierra Leone.

Various colored diamonds.  Image from the Gemological Institute of America.

Various colored diamonds.  Image from the Gemological Institute of America.

Until quite recently, the Mir mine in Siberia was also a major producer of diamonds.  The mine began its operations in the 1950s and closed in 2004. And while diamond mining operations in South America are considered small by global standards, they are notable for colored diamonds: Brazil produces large, fine quality diamonds, including intense pinks and green diamonds come from Guyana. There are also diamond mines in China -- and there used to be one in the western part of the United States. The Kelsey Lake diamond mine on the Colorado-Wyoming border, however, is longer in operation.
 
Diamond professionals use the grading system developed by GIA in the 1950s, which established the use of four important factors to describe and classify diamonds: Clarity, Color, Cut, and Carat Weight.

Color. Even the slightest of difference in color can dramatically af­fect diamond value. For example, two diamonds of the same clarity, same weight, and same cut can differ in value based on color alone. Completely colorless is the "ideal" diamond color.

Diamonds actually come in many colors. The normal range of color is colorless to light yellow and brown. Within that range, colorless diamonds are the most rare, so they’re the most valuable. They set the standard for grading and pricing other diamonds in the normal color range.

The GIA D-to-Z scale is the industry standard for color-grading diamonds. Each letter represents a range of color based on a diamond's tone and saturation.

To eliminate the guesswork from grading a diamond’s color, graders compare it to masterstones that represent known colors in the GIA D-to-Z scale. Image from the Gemological Institute of America.

To eliminate the guesswork from grading a diamond’s color, graders compare it to masterstones that represent known colors in the GIA D-to-Z scale. Image from the Gemological Institute of America.

Some diamonds emit a light called fluorescence when exposed to ultraviolet (UV) radiation. UV radiation is invisible to our human eyes -- and it is everywhere. Think: sunlight! 

Fluorescence can manifest itself in many different colors but blue is the most common in gem-quality diamonds.  The appeal of a strong blue fluorescence in a diamond is that it can cause a light yellow diamond to look white or closer to colorless in sunlight. Since blue and yellow are color opposites and tend to cancel each other out, the blue fluorescence helps to cancel the yellow color.

However, you can have too much of a good thing.  Too much fluorescence can cause a diamond to take on a cloudy appearance.  This has a negative effect on the value of the diamond.


Clarity. Clarity describes a gemstone's inclusions and blemishes.  The fewer the imperfections in a diamond, the higher the clarity. Diamonds can have internal flaws called inclusions or surface blemishes such as nicks and scratches. Once in a while, another tiny diamond or other mineral crystal can be trapped inside a diamond when it forms. 

This image from the Gemological Institute of America shows how a heart-shaped garnet was partially trapped inside a larger diamond during its formation.

This image from the Gemological Institute of America shows how a heart-shaped garnet was partially trapped inside a larger diamond during its formation.


Although inclusions may detract from a diamond's value, they do have positive effects. Inclusions can:

  • indicate to a gemologist that a diamond is genuine rather than synthetic
  • act as "birthmarks" to identify individual stones
  • provide clues to scientists about the formation of diamonds

Natural flawless diamonds are terribly rare and, so, terribly expensive. 


The GIA clarity grading system has eleven grades: Flawless, Internally Flawless, Very, Very Slightly Included (2), Slightly Included (2), and Included (3).

The size, number, position, nature, and color or relief of a clarity characteristic are taken into account by the diamond grader when assigned a grade. The importance of each characteristics will vary from diamond to diamond. For example, an inclusion off to the side of a stone would have less impact on clarity than the same size inclusion located directly under the table. In this case, the position is probably the determining factor.


 
The abbreviations, VVS, VS, SI, and I, have gained acceptance throughout the international diamond community. Their use is now widespread regardless of how the words they stand for translate into various languages. Very may translate to tres in French, for instance, but in France a very slightly included diamond is still a VS. Even a country like Russia, with a completely different alphabet, uses the same abbreviations.

Cut. A diamond is all about light.  And there is a great deal of science behind the cutting of a diamond to make the best use of light. A diamond cutter will use a variety of proportions to bring out a stone's brightness, fire, and scintillation.

  • brightness: white light reflections
  • fire: flashes of color
  • scintillation: areas of dark and light

Pattern is the relative size, arrangement, and contrast of bright and dark areas that result from a diamond’s internal and external reflections. There must be enough contrast between the bright and dark areas to give the pattern a crisp, sharp look.

As a general rule, the higher the cut grade, the brighter the diamond. Under fluorescent lighting, these diamonds (left to right) display high, moderate, and low brightness.

As a general rule, the higher the cut grade, the brighter the diamond. Under fluorescent lighting, these diamonds (left to right) display high, moderate, and low brightness.

The term “cut” also can describe a fashioned diamond’s shape. Shapes other than the standard round brilliant are called fancy cuts. The best known are the marquise, princess, pear, oval, heart, and emerald cut.
 

gia cut scale.jpg

Carat. The weight of a diamond is given in metric carats, abbreviated “ct.” One metric carat is two-tenths of a gram and a little more than seven thousandths of an ounce. One ounce contains just under 142 carats. Dizzy?  Let's put it this way: a small paper clip weighs about a carat.

One metric carat is divided into 100 points. Diamonds are weighed to a thousandth (0.001) of a carat and then rounded to the nearest hundredth -- or point. If a diamond is over a carat, its weight will usually be expressed in carats and decimals. A 1.03-carat stone, for example, would be described as “one point oh three carats.” Weights for diamonds that weigh under a carat are usually stated in points. A diamond that weighs 0.83 carat is said to weigh “eighty-three points,” or called an “eighty-three pointer.”

This diamond is over 100 carats!  From the Gemological Institute of America.

This diamond is over 100 carats!  From the Gemological Institute of America.

Large diamonds are more rare than small diamonds. The more scarce something is, the more it is worth. So a larger stone doesn’t just cost more. It also costs more per carat. A 1-carat diamond weighs the same as four 0.25-carat diamonds. But even if all the other quality factors are equal, the larger diamond is worth much more than the sum of the four smaller diamonds.

Carat weight can also be symbolic. While the visual difference between a 0.98-carat diamond and a 1.01-carat diamond is negligible, many people will opt for the larger stone—even at a much higher price.  The fact that the second stone is slightly over the “magic” one-carat size can give it as much as a 20 percent difference in price with only a 3-point difference in weight.

Historical notes and other interesting facts about diamond

Hard as a rock. Diamonds are the hardest material on earth? By far! They are 58 times harder than anything else found in nature.

Precious in the fist century. In the first century AD, the Roman naturalist Pliny stated: “Diamond is the most valuable, not only of precious stones, but of all things in this world.”

And in medieval times. Diamond jewels were an intrinsic part of living nobly; they were a conspicuous emblem of wealth and were also believed by many to be endowed with magical powers.

Origins in India. As early as the 4th Century B.C., India's diamond resources yielded limited quantities for an equally limited market: their own wealthy classes. Gradually, though, this changed. Eventually, Indian diamonds found their way, along with other exotic merchandise, to Western Europe in the caravans that traveled to Venice’s medieval markets. By the 1400s, diamonds were becoming fashionable accessories for Europe’s elite.

Untamed. The diamond takes its name from the Greek adamas, meaning invincible or untamed.

A talisman for bad dreams. Gems have always been considered natural talismans because of their brilliance and hardness; diamonds were thought to provide courage, as well as protection from nightmares.

Too hard to cut. Because of the cutting difficulties posed by the hardness of diamonds, they were not commonly used in rings, and then only in their natural pointed, crystal shape.

Diamonds discovered in Brazil! In the early 1700s, as India’s diamond supplies began to decline, Brazil emerged as an important source. Diamonds were discovered in the pans of gold miners as they sifted through the gravels of local rivers. Once it reached its full potential, Brazil dominated the diamond market for more than 150 years.

Modern markets. The story of the modern diamond market really begins on the African continent, with the 1866 discovery of diamonds in Kimberley, South Africa. Entrepreneur Cecil Rhodes established De Beers Consolidated Mines Limited 22 years later, in 1888. By 1900, De Beers, through its mines in South Africa, controlled an estimated 90 percent of the world’s production of rough diamonds

Not without color. Diamonds occur naturally in a variety of colors: colorless, yellow, brown, black, blue, green, pink, and, extremely rarely, red.

Resources and further reading

The Gemological Institute of America's Gem Encyclopedia.

Gemstones of the World. By Walter Schuman.  Our go to book at Grimballs.

Jewels: A Secret History. By Victoria Finlay.  An non-fiction adventure through time and place exploring the history of gems.

Smithsonian Institution National Museum of Natural History's Gem Gallery.