Diamond Composition
What is a diamond?
The diamond is a rare mineral, of natural origin, composed of carbon. Each carbon atom in a diamond is surrounded by four other carbon atoms and connected to them by strong covalent bonds - the most powerful type of chemical bond. This simple, uniform, and closely linked arrangement allows for one of the most durable and versatile substances known.
The diamond is the hardest known natural substance. It is also resistant to chemicals and has the highest thermal conductivity of all natural materials. These properties allow it to be used as a cutting tool and for other uses where durability is required. The diamond also has special optical properties, such as a high refractive index, high dispersion, and adamantine luster. These properties contribute to making the diamond the most popular gemstone in the world and allow it to be used in special glasses where durability and performance are required.
Since the diamond is composed of the carbon element, many people think that it must have formed from coal. This is still taught in many classrooms, but it's wrong!
| Chemical Classification | Native Element: Carbon |
|---|---|
| Color | Most diamonds are brown or yellow in color. The jewelry industry has favored colorless diamonds or those whose color is so subtle that it is hard to notice. Diamonds with vivid hues of red, orange, green, blue, pink, purple, violet, and yellow are extremely rare and sell at high prices. Some white, gray, and black diamonds are also cut and used as gemstones. Most industrial-quality diamonds are brown, yellow, gray, green, and black crystals that do not have the color and clarity necessary to be a beautiful gemstone. |
| Hardness | The diamond is harder than a streak plate. Its scratch is said to be "null" or "colorless". |
| Luster | Adamantine - the highest level of brilliance for a non-metallic mineral. |
| Diaphaneity | Transparent, translucent, opaque. |
| Cleavage | Perfect octahedral cleavage in four directions |
| Mohs Hardness | 10. Diamond is the hardest known mineral. However, the hardness of diamond is directional. It is hardest parallel to its octahedral planes and softest parallel to its cubic planes. |
| Specific Gravity | 3.4 to 3.6 |
| Diagnostic Properties | Hardness, thermal conductivity, crystal form, refractive index, specific gravity, and dispersion. |
| Crystal System | Isometric |
| Uses | Gemstones, industrial abrasives, diamond windows, speaker domes, heat sinks, low-friction micro-bearings, wear-resistant parts, dies for wire manufacturing. |
Where do diamonds come from?
Diamonds are not born on the Earth's surface. They form at high temperatures and pressures in the Earth's mantle, about 160 km below the Earth's surface.
Most diamonds that have been discovered were delivered to the Earth's surface by deep volcanic eruptions. These eruptions begin in the mantle, and as they rise, they tear off pieces of mantle rock and deliver them to the Earth's surface without melting them. These blocks from the mantle are known as xenoliths. They contain diamonds that formed under the high temperature and pressure conditions of the mantle.
People produce diamonds by mining the rock that contains the xenoliths or by mining the soils and sediments that formed when the diamond-bearing rocks weathered.
It is thought that some diamonds form under the high temperature/pressure conditions of subduction zones or asteroid impact sites. Some are delivered to Earth in meteorites. No commercial diamond mine has been exploited in deposits of these origins.
Gem diamonds for jewelry use VS industrial diamonds
Gem diamonds are diamonds whose color and clarity destine them for jewelry or investment. These diamonds are rare and represent only a small part of the world's diamond production. Gem diamonds are sold for their beauty and quality.
Natural diamond crystals have a specific gravity that varies between about 3.4 and 3.6. This range exists because most diamonds contain impurities and have irregularities in their crystal structure. Gem-quality diamonds are the most perfect diamonds, with a minimum of impurities and defects. Their specific gravity is very close to 3.52.
The diamond as a precious stone
Diamonds are the most popular gemstones in the world. Often, more money is spent on diamonds than on all other gemstones combined. The popularity of the diamond is partly due to its optical properties, that is, the way it reacts to light. Other factors are its durability, fashion, customization, and the aggressive marketing of diamond producers. The diamond is the birthstone for the month of April.
Diamonds have a very bright luster - the highest non-metallic luster - called "adamantine". This high luster gives them the ability to reflect a high percentage of the light that strikes their surface. This is one of the properties that give diamond gemstones their "sparkle". In addition, when a diamond is shaped into a gemstone, the angles of the facets are planned to reflect a maximum amount of light on its internal surfaces.
The diamond also has a high dispersion. When white light passes through a diamond, this high dispersion causes the separation of this light into its different colors. Dispersion is what allows a prism to separate white light into spectrum colors. This dispersion property is what gives diamonds their colorful "fire".
Quality of diamonds and precious stones
The quality of a diamond that has been faceted into a gemstone is primarily determined by four factors: color, cut, clarity, and carat weight. A standardized method of evaluating diamond quality was developed in the 1950s by the Gemological Institute of America and is known as "The 4Cs of Diamond Quality".
Color: Most gem-quality diamonds are colorless or slightly yellow, brown, or gray. The most appreciated and valuable diamonds are those that are completely colorless. These are the ones that are sold at the highest prices. However, another category of diamond gemstones is gaining popularity. These are colored diamonds, which come in a variety of shades, including red, pink, yellow, orange, purple, blue, green, and brown.
The value of colored diamonds is based on the intensity, purity, and quality of their color. Those whose color is saturated and vivid are called "fancy color diamonds" or "fancies". On average, only one diamond in 10,000 has a color that deserves the designation of "fancy". This rarity makes fancy color diamonds extremely valuable. Some of them have been auctioned for more than a million dollars per carat. They are among the most valuable and spectacular diamonds in the world.
Clarity: The ideal diamond is free of fractures and inclusions (particles of foreign matter in the gem). These detract from the appearance of the stone and hinder the passage of light. When they are present in large numbers, dark in color, in obvious positions or sizes, they significantly degrade the appearance of a cut gem and decrease its value. They can also reduce the stone's resistance.
Cut: The quality of the design and craftsmanship used to cut a diamond is what determines its appearance. The angles at which the facets are cut, the proportions of the design, and the quality of the polish determine its appearance, brilliance, sparkle, pattern, and fire. Ideal stones are perfectly polished to be highly reflective and emit maximum fire. Corresponding faceted faces are of equal size and identical shape. And the edges of each facet perfectly join with each of its neighbors.
Carat: Diamonds are sold by the carat (a unit of weight equal to 1/5th of a gram or 1/142nd of an ounce). Small diamonds generally cost less per carat than larger stones of equal quality. This is because very small stones are very common and large stones are exceptionally rare.
Diamonds used as abrasives
Diamonds being very hard (ten on the Mohs scale), they are often used as abrasives. Most industrial diamonds are used for this purpose. Small diamond particles are incorporated into saw blades, drill bits, and grinding wheels. These tools are then used to cut, drill, or grind hard materials. They can also be reduced to a fine powder and turned into a "diamond paste" used for very fine grinding or polishing.
As early as the 16th century, gem cutters began using small diamond particles to cut and polish other diamonds. Diamond is the only abrasive capable of doing this job. Today, in the 21st century, lasers are used to cut many diamonds, but small diamond particles are still used for diamond polishing.
The global demand for industrial diamonds far exceeds the supply that can be obtained through mining. A shortage of diamond abrasives began to manifest during World War II. In the 1950s, methods of producing synthetic diamonds were discovered. Quickly, the methods of manufacturing synthetic diamonds became so efficient that synthetic diamond abrasives were more reliable and cheaper than diamond abrasives made from natural diamonds. Today, synthetic diamond abrasives are manufactured in hundreds of factories and their cost is less than 1 dollar per carat - and they perform just as well as abrasives made from natural diamonds in industrial use.
Other uses of diamonds
Most industrial diamonds are used as abrasives. However, diamonds are used in many other applications.
Diamond windows are made from thin diamond membranes. They are used to cover the openings of lasers, X-ray machines, and vacuum chambers. They are transparent, very durable, and resistant to heat and abrasion.
Diamond speaker domes enhance the performance of high-quality speakers. Diamond is a very rigid material, and when it is transformed into a thin dome, it can vibrate quickly without undergoing deformation that would degrade the sound quality.
Heat sinks are materials that absorb or transmit excess heat. Diamond has the highest thermal conductivity of all materials. It is used to keep heat away from heat-sensitive parts of high-performance microelectronics.
Low-friction micro-bearings are needed in small mechanical devices. In the same way that some watches have ball bearings in their movements, diamonds are used when extreme resistance to abrasion, durability, and reliability are needed.
It is possible to produce wear-resistant parts by coating the surfaces with a thin layer of diamond. In this process, carbon is transformed into a vapor that deposits the diamond on the surface of the parts prone to wear.
Is the diamond hard?
Although diamond is known as the hardest natural material in the world and has been assigned a hardness of 10 on the Mohs hardness scale, this information is an oversimplification. The hardness of diamond crystals varies depending on their direction.
The direction of greatest hardness is parallel to the octahedral crystal planes. When diamond crystals are cut and polished into gemstones, it is very difficult to cut them in this direction with a diamond saw. That's why, instead of using a diamond saw or the traditional practice of breaking them by cleavage, much of this work is now done by laser sawing.
Facets cut parallel to the direction of the octahedral crystal are also difficult to polish, so cutters change direction or risk leaving a "lizard skin" texture on the facet.
The softest direction in a diamond crystal is parallel to the cubic planes. The best polishing is done on facets that are parallel to this direction. Although this is the softest direction in a diamond, its hardness is several times greater than that of corundum, the second hardest mineral on the Mohs hardness scale.
Diamond simulants
Diamond simulants are materials that resemble diamonds, but have a different chemical composition. Diamond simulants can be natural materials such as colorless zircon or sapphire. Most often, they are man-made materials, such as cubic zirconia (ZrO2), moissanite (SiC), YAG (yttrium aluminum garnet Y3Al5O12) or strontium titanate (SrTiO3).
Synthetic diamonds
Diamond is a very precious material, and people have been working for centuries to create them in laboratories and factories. Synthetic diamonds are man-made materials that have the same chemical composition, crystal structure, optical properties, and physical behavior as natural diamonds. Other names used for synthetic diamonds include: "lab-grown", "lab-created" and "man-made". These names clearly indicate that the diamonds did not form naturally in the Earth, but were created by man.
The first successful commercial synthesis of diamond was achieved in 1954 by workers at General Electric. Since then, many companies have managed to produce synthetic diamond suitable for industrial use. Today, the majority of industrial diamond consumed is synthetic, with China being the global leader with a production of over 4 billion carats per year. Most major industrialized nations are now able to produce synthetic diamonds for industrial use in factories.
Over the last decade, several companies have developed technology that allows them to produce lab-created gem-quality diamonds, up to a few carats in size, in several different colors, including colorless. Some companies use high-pressure, high-temperature methods - these are then referred to as HTHP diamonds. Others create diamonds using a chemical vapor deposition process, the CVD diamonds. These man-made gemstones are sold in jewelry stores and online at a significantly lower price than natural stones of similar quality and size. They have a beautiful appearance and an attractive price. Synthetic diamonds must be sold with a mention allowing the buyer to clearly understand that they were man-made.
Will consumers accept synthetic diamonds?
Synthetic diamonds have been the dominant type of diamond in industrial applications since the end of the 20th century. Most of the diamonds used to make abrasives and cutting tools are now synthetic. Almost all of the diamonds used to make windows, speaker domes, heat sinks, low-friction micro-bearings, wear-resistant parts, and other technological products are now synthetic.
Synthetic diamonds used for these purposes are much less expensive than mined diamonds, have more consistent properties, and are increasingly available in custom specifications. There is no emotional barrier to synthetic diamonds replacing mined diamonds in these uses.
In the jewelry sector, the willingness of consumers to accept synthetic diamonds is a subject of considerable debate. Some believe that jewelry consumers want "real diamonds", that is, "mined diamonds". Others believe that synthetic diamonds will appeal to those who are uncomfortable with the human rights and environmental issues associated with some mined diamonds. However, the real motivating factor will likely be price. Currently, many synthetic diamonds intended for jewelry have a price advantage of 30 to 40% over mined diamonds. This is probably what will most encourage consumers to accept synthetic diamonds.
Observation and speculation.... If you walk into almost any mall jewelry store and look in the cases where rubies, sapphires, and emeralds are sold, you will often see that most of the stones offered are synthetic. A very untrained person can often recognize them by their bright color and superb clarity. Synthetic materials have a superior appearance, and their prices are low compared to natural gems of similar size and apparent quality. Consumers get a better look for a lower price, and the majority of them accept this deal at the low end of the price range.
The battle for emotion and sales dominance in the market for popularly priced rubies, sapphires, and emeralds was won by synthetics decades ago. Over the next decade, the diamond market could also evolve in favor of synthetic products. This is already the case, as synthetic diamonds are taking a very visible place in the market. The price of synthetic diamonds will likely decrease as more and more machines to produce them are put into service, become more efficient, and competition among manufacturers intensifies. Eventually, the price difference between natural and synthetic diamonds will be greater than many customers can ignore, and they will buy synthetics. If the next world-class advertising campaign promotes synthetic diamonds, a huge shift in consumer demand could occur.
This world-class advertising campaign could be that of Lightbox, which offers "white" and colored diamonds at the unheard-of price of 800 dollars per carat.
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