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What is a Diamond and where are they found?

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Introduction

What is a Diamond and where are they found? Diamonds are the hardest known mineral, comprising of crystalline carbon, formed under intense heat and pressure. Diamonds are found in ancient volcanic pipes, mainly in South Africa and Siberia, and in deposits off the coast of Namibia. Over 80% of diamonds mined are used in industry mainly for cutting and grinding tools. Others are used in jewellery and in industry. Diamond Structure and Bonding * In diamond, each c-atom is covalently bonded to four other c-atoms to give a tetrahedral unit. * In diamond c-c-c bond angle is 109.5 o (degrees). These basic tetrahedral units unite with one another and produce a cubic unit cell. A diamond is a giant molecular structure containing many of these tetrahedral units making it very rigid. * On a scale of ten for hardness diamond is 10. This is called Moh's scale. To compare this to other materials gold has 2.5, pearls have 3.5 and sapphires and rubies have 8. * c-c bond length in diamond is 1.54 Ao (Angstroms, this is 10 to the power of -10 m or 15.4 nano metres). * c-c bond energy is 347 kj/mole. * In a diamond crystal basic units join to form a octahedral shape of diamond crystal. This means it has eight sides. * * What are the properties of Diamond? * * Diamond is transparent over a larger range of wavelengths (from the ultraviolet into the far infrared) ...read more.

Middle

Dr Shirey said in a private interview for the BBC, and I quote, "We believe that the Earth is not forming as many or as big diamonds as it did billions of years ago. Perhaps the planet was hotter on the inside, or the composition of the rocks was subtly different. Whatever it was it has changed now. Diamond formation was chiefly a feature of the Earth's youth." This information is published in the journal Science. Do planets make diamonds from methane? 1 October 1999 The high temperatures and pressures found in the middle layers of Neptune and Uranus might be capable of converting methane into diamond. Physicists in the US have recreated the high temperatures and pressures inside the planets in a laser-heated diamond anvil cell. They found that the methane molecules fall apart under these conditions to form complex hydrocarbons and diamond. The results have implications for theories of planetary formation and evolution (Science 286 100). Scientists have long suspected that the core of the outer planets could consist of diamond, but this is the first evidence for diamond formation in the middle layers of the planets. Both Neptune and Uranus consist of 10-15% methane and, according to Benedetti and colleagues, large quantities of diamond could affect both the luminosities and magnetic fields of the planets. Total Internal Reflection in Diamonds If the angle of incidence is increased beyond the critical angle, the light rays will be totally reflected back into the incident medium. ...read more.

Conclusion

Since 1960, companies in a number of countries have produced synthetic diamonds on a commercial scale. In 1990 a new synthetic process was developed that makes diamonds that are harder, heavier, and better heat conductors than natural diamonds. It is important to remember that a synthetic gemstone is one that carries all of the chemical, structural, and colour properties of the natural, but it is synthetically grown in a laboratory. And will therefore not cost near as much as a natural gemstone because it is not as rare and not as valuable. Modern manufacture of synthetic diamonds utilizes these same methods discovered by Mr. Hall. A mixture of graphite and a catalyst (typically nickel) is subjected to a pressure of approximately 1,000,000 pounds per square inch and a temperature of 1,800 �C for a period of approximately 1 hour. During this time diamond crystals nucleate at many sites in the mixture. The mixture is then cooled and the pressure reduced. The diamond crystals are then separated from the remaining graphite and nickel using an acid wash. The separated crystals are sorted by shape, size, and impurities. This process is called grading. A typical production cycle will yield approximately 300 carat of synthetic industrial diamond of various grades. The larger diamonds are used for sawing concrete, granite, and marble. Smaller diamonds are used in grinding wheels. Most synthetic diamonds are not sold as gemstones for jewellery but are used industrially. This is because those diamonds made are generally of lower quality than the naturally created ones. This means that the trade in synthetic diamonds does not really affect the global prices of diamonds in the market place. ...read more.

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