Diamonds are stones made of pure carbon with a cubic crystallize structure. These are considered a precious gemstone that have several remarkable characteristics:
HardnessDiamonds are the hardest known material. For example, diamonds can scratch anything but only diamonds can scratch other diamonds. For this reason, the hardness of materials is commonly tested by scratching them with a diamond with fixed pressure and time and then measuring the size of the scratch.
StructureDiamonds have a crystal structure known as diamond cubic that is a repeating pattern of 8 atoms with a cube-like form. The structure of diamonds is remarkably rigid.
ToughnessDiamonds aren't particularly tough and can be easily fractured. For example, a diamond can be crushed with one hit from a regular hammer. This is due to their hardness and rigid crystalline structure. For example, rubber is tougher than a diamond due to its flexible structure that bounces back from stresses.
Thermal ConductivityDiamonds have the highest thermal conductivity of any natural material. This property is often used to authenticate diamonds.
CombustibilityAs carbon, diamonds will burn at high temperatures in the presence of oxygen. Diamonds will ignite around 900 degrees Celsius or 1,652 degrees Fahrenheit. For this reason, jewelers must be careful using molten metal to mount a diamond, as this is hot enough to ignite the stone. Diamonds can also burn in a house fire.
Compressive StrengthDiamonds are the least compressible of all natural materials and have high compressive yield strength.
Optical DispersionDiamonds have prized optical properties and are particularly known for dispersion of light into different colors. This gives diamonds their characteristic sparkling appearance.
RarityDiamond production is around 130 million carats a year and gem quality diamonds aren't particularly rare as compared to other precious gemstones. Perceptions of the rarity of diamonds has been greatly influenced by marketing. This being said, extremely high quality diamonds, particularly large flawless stones, are certainly rare.
ValueDiamond jewelry tends to have low resale value relative to its retail cost. For this reason, diamond jewelry shouldn't be viewed as an efficient store of wealth. As with other gemstones, the value of diamonds is evaluated according to factors known as the 4Cs as follows.
|Carat||The weight of the diamond. The price can jump dramatically at certain psychological points. For example, a 1.00 carat diamond might be worth much more than a 0.99 carat diamond.|
|Clarity||A lack of internal defects known as inclusions. This is often measured by looking at the diamond at 10x magnification. Diamonds with obvious inclusions are typically considered industrial grade.|
|Color||For normal diamonds, completely colorless stones are most valuable. For example, a slight yellow tinge would lower a diamond's value. The exception to this is colors that are viewed as valuable known as fancy diamonds. These are separately valued according to less clear rules.|
|Cut||The quality of workmanship and the angles to which a diamond is cut. This is based on well understood traditions. It is difficult for a consumer to evaluate this factor on their own.|
Industrial DiamondsAround 80% of mined diamonds are considered industrial grade. These are commonly used for tools, machines and industrial equipment.
HistoryHistorically diamonds were quite rare and were considered one of the cardinal gems alongside amethyst, emerald, ruby and sapphire. Around 1870, with the discovery of diamond deposits in South Africa, production increased dramatically leading to efforts to control the supply of diamonds and aggressively market them to the masses. Supply has only continued to increase since 1870 with large deposits found in Russia, Botswana, Australia, Congo, Canada and Angola.
ColorsDiamonds are typically colorless when composed of pure carbon. Due to their rigid structure diamonds are resistant to inclusions. However, they can contain impurities than give them color as follows.
Colored diamonds are known as fancy diamonds when the color is perceived positively such that they are more valuable than regular diamonds. These include blue, green, pink and red diamonds. Natural red diamonds are very rare. Unpopular and common colors such as brown and yellow are often viewed as industrial diamonds with exceptions such as large flawless stones that may have great value despite being a low grade color.
FluorescenceAbout 1/3 of colorless diamonds will glow a color when exposed to ultraviolet light such as strong sunlight. This is usually a blue color but can also be green, yellow, red or orange.
Black DiamondsBlack diamonds are known as Carbonado and have a fundamentally different internal structure than regular diamonds. Their origin is unknown and they were possibly formed in space by processes such as a supernova. The black color of carbonado is due to the presence of graphite and amorphous carbon in the stone.
Synthetic DiamondsSynthetic diamonds are manufactured or lab produced diamonds made of carbon. These can be designed to have superior properties to natural diamonds such as greater hardness or thermal conductivity. These are sold as gems but must be marketed with terms that indicate they are artificial. Synthetic diamonds can be created in various colors including extremely precious colors such as red.
Imitation DiamondAn artificial or natural stone with a composition other than pure carbon that looks like a diamond. For example, cubic zirconia is designed to look like a diamond but isn't nearly as hard with a mohs scale hardness of 8 compared to diamonds at 10.
Enhanced DiamondDiamonds that are processed to improve their perceived quality. For example, a brown diamond that is colored to appear to be a fancy diamond such as a blue diamond. It is also possible to remove inclusions and perform other treatments that may influence value.
HistoryDiamonds have been known to humans since prehistory and were used as both precious gems and as engraving tools in antiquity. The first diamond mines emerged in India up to 6,000 years ago. Diamonds were very rare until 1870.
MythologyA number of large diamonds are considered cursed according to myth. For example, the January 29, 1911 edition of the New York Times listed 14 people who had owned or worn the Hope Diamond who had met a terrible fate. This wasn't accompanied with any sources such that it is likely based on myth. Other famous diamonds such as the Black Orlov and Koh-i-Noor are associated with similar myths.
AgeMost diamonds are thought to be between 1 and 3.5 billion years old. Most were formed at a depth of 150 to 800 kilometers below the surface of the Earth. Economically viable deposits of diamonds have been transported closer to the surface by geological processes such as volcanic eruptions. It is a common myth that diamonds are made of coal, as diamonds are older and are formed at much greater depth than coal deposits.
SpaceDiamonds are thought to be quite common in space. Meteorites commonly contain particles of diamond known as nanodiamond. Diamonds can be formed by stars. The planets Uranus and Neptune are thought to have large amounts of diamond that have been formed with the compression of methane. It is also theorized that planets in other planetary systems may be almost entirely composed of diamond.
This is the complete list of articles we have written about gemstones.
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References† Have You Ever Tried to Sell a Diamond?, Edward Jay Epstein, The Atlantic, February 1982.Ariovich, G. "The economics of diamond price movements." Managerial and Decision Economics 6.4 (1985): 234-240.Janse, A. J. A. "GLOBAL ROUGH DIAMOND PRODUCTION SINCE 1870." Gems & Gemology 43.2 (2007).
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