The Diamond: Composition, History, Uses, and Synthesis

ABSTRACT

This paper provides an in-depth look at the diamond. It is specifically structured to follow the journey a diamond takes, from its birth as carbon, through its mineral state, to that of the well-recognized gemstone to elaborate on its history and physical makeup. The paper begins with an introduction, which provides a comprehensive look at the internal workings of the diamond mineral. Specific attention is paid to the diamond’s various singular qualities that make it remarkable, especially when compared to other minerals. Following the introduction is a history of the diamond, beginning with its own start and tracing until it came to the attention of humanity. Examples of various large-scale diamond discoveries are highlighted, as well as current issues to give the reader an awareness of the hold diamonds have on modern society. The next section covers the human use of the diamond—everything from simple jewelry to diamond-tipped drills is discussed. Finally, diamond synthesis is explored—both natural and laboratory. The conclusion provides a summary of these issues and a venue for discussion regarding the overall impact the diamond has had on humanity. It is, after all, a mineral that people are willing to kill for.

INTRODUCTION

When one thinks of a diamond, what comes to mind is usually a large, glistening, multi-faceted gemstone, but anyone with even the slightest scientific background knows that this is not how diamonds occur naturally. The journey from mineral to gemstone is a long, involved process. Most people understand how remarkable the diamond is just from its appearance. There are reasons, after all, that it the preferred stone for an engagement ring. Once one learns how diamonds come to be, and how they get to their conventionally known appearance from the rough mineral they start out as, it becomes clear how truly remarkable the diamond is, appearance aside.

Physical Composition. To begin with, the physical makeup of the diamond mineral is extraordinary. George E. Harlow’s 1998 work, The Nature of Diamonds1 provides a detailed analysis of the physical properties of the diamond and just how these physical properties cause the diamond to exist in the form it does. It is a mineral that, like many other minerals, is composed of carbon. It shares this commonality with other minerals, which include Lonsdaleite—which is very rare— graphite—which is a much more common mineral—and according to Diamond Deposits: Origin, Exploration, and History of Discovery, published in 2009 by Edward Erlich and Dan Hausel2, with chaoite—which is a type of graphite that exists only at very high temperatures. All of these minerals are made from carbon, but, for the most part, this is where the similarities end.

As Harlow explains, diamonds differ from these other carbon-based minerals for a number of reasons, but the most crucial is in the arrangement of its atoms, which allow for its crystal structure1. The diamond, like all crystals, is formed through a repeated pattern of elements or compounds. Oftentimes, this pattern allows for “external plane faces” which give the diamond its distinctive shape1. All diamonds are isometric (i.e., cubic in their formation) but show variation within this basic shape2. Erlich and Hausel list the various forms in which the diamond’s isometric shape may present itself, including octahedron (presenting with eight equal sides) and dodecahedral form (presenting with twelve sides—this shape is rarer than the others). They continue to explain that flattened crystals, or crystals with elongated bodies, often occur naturally as well2. Harlow adds more information to this, explaining that the flat facets, characteristic of the diamond, will be impeded if there is insufficient space in the diamond’s environment, but that it is still classified as a crystal1. He also explains that some destructive processes have the ability to cause the diamond to form itself into a much more rounded object, but he is adamant in his assertion that “nonetheless, that, too, is still a crystal”1.

Special Properties. The diamond is set apart from other minerals for a variety of reasons. It has a very specific structure, which allows for its superlative qualities. Because the diamond is composed (nearly) entirely of carbon, it makes covalent bonding occur in such a way that each atom of carbon bonds to four other adjacent atoms of carbon through one shared electron. Covalent bonding to such a great extent is extremely rare, and it is the cause of diamond’s high ratings of hardness and conductivity1.

Hardness. Measuring a diamond’s level of hardness is difficult, especially on the Mohs scale (the standard scale for measuring a material’s hardness). The diamond does register as number 10 on the Mohs hardness scale, which is the highest level assigned, but because there are no other minerals as hard as the diamond, it can only be measured against itself1. Harlow explains that, although the diamond has a reputation for being the hardest of all minerals, it does show variation in its hardness. Some diamond shapes, in general, are more durable than others, but even with shape, a difference can often be detected. Harlow writes that in an octahedron, the corners are easier to grind down than are the flat planes of the face. “Indeed,” he writes, “the earliest gem-cut diamonds make it clear that the faceters were aware of that”1. This variation in hardness leads to the diamond’s equally rare variation in another important quality: cleavage.

Cleavage. Cleavage refers to a diamond’s ability to be split along a flat plane. Rather than splitting or fracturing, cleaving leaves a smooth surface. The irregular or curved mineral will often split or fracture, but because diamonds form flat planes, when split, they cleave instead1. As Erlich and Hausel describe, the diamond’s cleavage is perfectly octahedral due to the fact of its cubic covalent bonding, which leaves one straight line of single bonds between the planes of the diamond’s surface2. This area of single bonding allows for the diamond’s one line of weakness.

Varieties. In addition to the basic shape variation of diamonds (i.e., cube, octahedron, and tetrahedron) they are also broken down into ten distinct categories, outlined by Erlich and Hausel. The fist variety, Variety I, is the most common. It accounts for ninety-eight to ninety-nine percent of the diamonds known to be in existence. Variety I diamonds are plane-faced and octahedral in shape. Variety II is also plane-faced, though cubic, rather than octahedral, in shape. They are most notably recognized for their coloring, which is green or amber. Variety III diamonds are also cubic but vary in their coloring which is gray or dark in color. This coloring results from impurities stemming from nitrogen deposits. Variety IV diamonds are similar to Variety I but are known for their uneven color (i.e., zoning) which can be seen clearly by the human eye. Variety V diamonds are rounded. They are transparent in the center, but show color imperfections on the outer edges, due to graphite deposits. Variety VI diamonds are perfectly spherical in shape, except for rare pear-shaped specimens. Varieties VII, VIII, and IX are known best for their impurities. Variety VII is “yellowish” and presents with cracks or other imperfections. VIII is irregularly shaped and tends to form lumps. IX is similar but is either dark gray or black in color. Variety X is better described as a collection of diamond crystals that form one large dark shape, known as carbonado. It is important to note that, despite their wide range of differences, these varieties are still very much considered crystals in general and diamonds in particular.

HISTORY

The diamond has a rich and complex history that begins before Christ or Buddha ever walked the earth. According to Joan Dickinson’s The Book of Diamonds, the first people to have come across diamonds were India's Dravidians. Dickinson states that the Dravidians discovered diamonds some seven or eight centuries before Christ, and even two or three before Buddha. It is these Dravidians who provided a name for the measurement still used for diamonds today—“the carat.3” Because they believed diamonds grew in the ground similar to root vegetables like turnips, they would use carob tree seeds as a comparison of weight. These seeds were known as “cattie” or “carat,” and thus the unit of measurement was named as such3.

Diamonds have been considered precious for such a long time that legends have been told about them for centuries. Dickinson recounts her favorite story regarding Alexander the Great and his encounter with a diamond pit. When, according to a story told by Aristotle’s alleged nephew, Alexander and his men found a pit full of diamonds and deadly snakes, Alexander ordered the men to kill sheep and throw them into the pit. The diamonds adhered to the sheep’s’ skin, and when vultures came to eat the flesh, the birds flew away carrying the carcasses and the embedded diamonds. And, as Dickinson writes, “Behind them Alexander's men ran, picking up the diamonds that fell and following the vultures to their mountain roosts to garner the rest”3, It is difficult to gauge the validity of this story. Dickinson explains that diamonds do stick to fat and that vultures do eat dead flesh—the story is improbable, but not impossible3. Either way, this story is important because it demonstrates the allure diamonds have held for people since they were discovered.

The legendary history of the diamond may have much to do with the discrepancies that exist regarding where exactly the earliest diamonds were found. Dickinson Some experts believe that they came from a city in India known as Golconda. This is because the diamond trade has its roots here, and there is a possibility that a diamond mine existed along the Godavari river, located there3. Dickinson explains that while the Golconda theory is sound, there are others who believe that the Kristna River may have been home to the first diamonds mines because this is where diamonds were found during the medieval period3. However, diamonds were also found in Borneo around 600 AD. This site is particularly interesting because it is still guarded with extreme care and is treated as a very spiritual place. In fact, when a new pit is opened, an animal sacrifice is held and workers may not speak louder than a whisper for fear they will anger evil spirits3. Again, even the stories regarding diamonds today are full of mystery.

Dickinson writes that the Bible is the first place where we see references to diamonds in the Western world, though, she continues, this is likely due to confusion between diamonds and rock crystal. Dickinson’s discussion explains the many ways that the early people who studied them allowed the diamond’s infamous nature to inform their understanding. Some believed, for example, that the true test of a diamond is whether or not it can be crushed with a hammer. We know now that diamonds, of course, can be crushed—quite easily in fact, if their cleavage is taken into account. Pliny the Elder, a Roman author of the time believed that diamonds could be melted if soaked in the blood of a goat and that eating a diamond would neutralize poison.3 This is another example of the tall tales that built up around diamond lore—In contrast, in India, it was believed that diamonds were uses primarily as poison.3

For many centuries, these legends are the only accounts we have to go on regarding the start of the diamond trade. What we do know, according to Dickinson, is that for twelve long centuries, the only place to find diamonds was in the Far East. Trade, in general, was lucrative in that area, and diamonds would travel along with coveted ginger and cinnamon and be sent along to Mediterranean or Ethiopia by way of the Persian Gulf and Arabia.3 Individuals were willing to travel a long way and pay a large amount of money for these diamonds.

The Gem Institute of America (GIA) explains that while India dominated the diamond market for centuries, its supply eventually began to run out.4 Around the same time, gold miners in Brazil began to see diamonds showing up as they were panning for gold. With India’s supply on the decline, it was fortunate that Brazil was able to get involved with the diamond trade when it did. According to GIA, Brazil was then at the head of the diamond game for over 150 years.4

The GIA argues that the history of the modern diamond doesn’t really begin until 1866. It is at this point in history that the diamond mines in Kimberley, South Africa were found. Eventually, the mines were purchased all together by a man named Cecil Rhodes, who then founded the De Beers Consolidated Mines, (though this would take 22 years)”.4 De Beers is a name we still know to be associated with diamonds—a testament to the company. This discovery of the mines, as the GIA explains, led to many changes in the diamond industry. The mines in South Africa were deeper underground, which meant that better techniques for mining had to be developed. It also meant that marketing, cutting, and polishing all advanced as these changes led to better efficiency, cheaper cost and better stones.4

The GIA devotes the next section of its history tracing the rise of the diamond industry from 1870 through to 1990 and beyond. This period of 120 years saw a jump from diamond production at under one million carats, to three million carats, to fifty million carats, and by 1990, more than 100 carats. This time period also saw Zaire and the former Soviet Union emerge as two of the biggest diamond producers (next to South Africa) in the world. The Jwaneng mine in Botswana also began to work in the diamond trade. By 2000, Northern Canada and Australia were also part of the industry.4

HUMAN USES

Diamonds, beautiful luster and shine aside, are extremely useful. In everything from anvil cells to face scrub, diamonds prove to be more than just pretty to look at.

Diamond Anvil Cell. David C. Rubie, Thomas S. Duffy, and Eiji Ohtani explain in their 2004 report, “New Developments in High-pressure Mineral Physics and Applications to the Earth's Interior” explain that a diamond anvil cell (DAC) is a specially developed tool used in scientific experiments. The DAC uses two diamonds in highly pressurized states. A DAC is beneficial when an experiment calls for extremely high pressures, such as the kind found at the center of the earth’s core. Diamonds are particularly useful here because they are extremely hard, can withstand extreme pressures, and are superconductors of electricity.5

Saw Blades. The International Trade Commission's study, “Diamond Sawblades and Parts Thereof from China and Korea” discusses the interest and use of diamonds in saw blades. Diamonds are particularly useful here because of their extreme hardness, which makes them ideal for cutting. The report lists various materials that are difficult to cut in general, but which become much easier to manage when up against the hardness of a diamond. These materials include stone, marble, brick, tile, asphalt, and cement.6

Polishing Powders. Australia’s governmental Department of Energy, Resources, and Tourism writes that diamonds are often ground down and used to shape and grind other metals, which are often too hard for minerals with lesser hardness than diamonds. They are used on optical surfaces, aircraft engines, and cutting tools. They are also used in drilling bits, building construction, and are used to cut roads, concrete, brick, and stone.7

SYNTHESIS

Natural Synthesis. Michelle and Ralf Tappert’s, Diamonds in Nature: A Guide to Rough Diamonds explain the conditions necessary for naturally occurring—cultured—diamonds. According to the writers, carbon atoms form to become various minerals based on the amount of pressure applied to the carbon deposit. Diamonds form when pressure on the carbon is higher than thirty thousand bars. When pressure is less than this, graphite forms8.

Because pressures this high do not exist anywhere even close to the surface of the Earth, diamonds occur naturally only underground, at depths of more than one hundred and forty kilometers. While diamonds do require higher pressures and levels deep underground, they also prefer lower temperatures. This means that in nature, ideal conditions for diamonds to occur are in areas with a very low geothermal gradient. Generally, these are areas that are in parts of the world more than 1.5 billion years old. Diamonds are believed to crystallize primarily from fluids passing through these areas that are rich with carbon.8 Because diamonds have such strict conditions necessary for their growth, scientists have devised ways to make laboratory-grown diamonds.

Laboratory Synthesis. Laboratory synthesized, or “man-made,” diamonds are actually fairly similar to naturally occurring diamonds, but the process to make them differs in many ways. Synthetic Diamond: Emerging CVD Science and Technology, written in 1994 by Karl Spear and John Dismukes, details the history and development of diamond synthesis which really begins with the first successful diamond synthesis. William Eversole reached this in 1952. Low-pressure chemical vapor deposition was used.9 C. G. Suit’s 1965 study, “Man-made Diamonds—A Progress Report”, explains that very high pressure and temperature are needed to create a lab-grown diamond, but that these are not the only two factors. Because certain metals act as a catalyst, introducing one into the process can enhance the rate needed as well as the amount of product with less effort.10

According to the Spear’s text, at first, many people claimed that lab-grown diamonds were physically identical to their cultured counterparts, but we know now that this is not the case. There are many different qualities between these two methods for diamond formation and the products they yield—the two most noticeable differences are the specific gravity of the stones (higher in the synthetic) and hardness, (harder in the natural) 9 but The Diamond Formula: Diamond Synthesis--a Gemological Perspective written By Amanda S. Barnard also points out that synthetic diamonds, unlike cultured diamonds, often contain metallic solids which all have rounded edges and form groups. They are usually color-less, though sometimes yellow.11 These imperfections make a laboratory diamond much easier to recognize.

Space Synthesis. While no consensus has been reached on this theory, it is important to include here because it does offer up the possibility of a third type of diamond synthesis. The earlier discussed carbonado is a type of diamond found only in America and South Africa.8 It’s location and formation make it difficult to tell for sure, but it does not appear to have originated on earth. One of the theories that, if not accepted, is at least entertained, is that these diamonds came to Earth already synthesized.8 If this were the case, then they would have traveled here on an asteroid, though the text clarifies that it would not have been the impact of this asteroid hitting Earth that would have caused the synthesis. Either way, it is incredible to consider the idea that there are diamonds on Earth that were not formed here.

CONCLUSION

Whether grown in a lab, occurring naturally, or even crash landing onto planet Earth from space, diamonds are fascinating in their ability to be so singularly different from other minerals—even those which share carbon as their building blocks. The diamond has so many characteristics that make it unique from other minerals, and the fact that these all occur because of one simple difference is astounding. Diamonds are harder than any other mineral; they are more durable, and they are incredibly complex.

Studying the diamond helps to illuminate the subject, of course, but it also provides insight into the inner-workings of all minerals. The diamond is a great example of how certain aspects of nature occur in such a way as to make themselves work seamlessly with the world. If it were not for the way carbon bonds with itself, the diamond would not be possible. The various legends and lore that surround the diamond are easy to understand when one considers the fact that diamonds have a long, involved history that predates even Christianity by a few centuries.

When one thinks about the fact that the diamond is the stone used in an engagement ring to signify commitment and eternity, it becomes clear just how important the diamond is. Even individuals who have no knowledge of the internal structure that makes the diamond so compelling still consider it worthy of admiration. Overall, following the diamond’s journey from rough mineral, to gemstone, or from rough mineral to anvil cell, or even from rough mineral to concrete saw, shows just how complex and versatile this very important mineral is.

CITATIONS

Harlow, George E.. The nature of diamonds. Cambridge, U.K.: Cambridge University Press in association with the American Museum of Natural History, 1998. Print.

Erlich, Edward, and W. Dan Hausel. Diamond deposits origin, exploration, and history of discovery. Littleton, CO: Society for Mining, Metallurgy, and Exploration, 2009. Print.

Dickinson, Joan. The Book of Diamonds. New York: Courier Dover, 2012. Print.

"Diamond History and Lore." Diamond History and Lore. Gem Institute of America, Inc., n.d. Web. 7 Mar. 2014. <http://www.gia.edu/diamond-history-lore>.

Rubie, D.c, T.s Duffy, and E Ohtani. "New Developments in High Pressure Mineral Physics and Applications to the Earth’s Interior." Physics of The Earth and Planetary Interiors 143-144 (2004): 1-3. Print.

Diamond sawblades and parts thereof from China and Korea investigation nos. 731-TA-1092-1093 (final).. Washington, DC: U.S. International Trade Commission, 2006. Print.

"Diamond Fact Sheet." Diamond. Department of Resources, Energy, and Tourism, n.d. Web. 8 Mar. 2014. <http://www.australianminesatlas.gov.au/education/fact_sheets/diamond.html#uses>.

Tappert, Ralf, and Michelle C. Tappert. Diamonds in nature a guide to rough diamonds. Berlin: Springer, 2011. Print

Spear, Karl E., and John P. Dismukes. Synthetic diamond: emerging CVD science and technology. New York: Wiley, 1994. Print.

Suits, C. G.. "Man-Made Diamonds: A Progress Report." The Physics Teacher 3.5 (1965): 220. Print.

Barnard, A. S.. The diamond formula: diamond synthesis - a gemmological perspective. Oxford: Butterworth-Heinemann, 2000. Print.