Diamond
In mineralogy, Diamond from the ancient Greek ἀδάμας – adámas "unbreakable") is a metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at standard conditions. Diamond is renowned as a material with superlative physical qualities, most of which originate from the strong covalent bonding between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material.
photo by:R. Tanaka
Pyramidal diamond anvil impactor on a Vickers hardness tester
Diamond is the hardest known natural material on both the Vickers and the Mohs scale. Diamond's hardness has been known since antiquity, and is the source of its name.
Diamond hardness depends on its purity, crystalline perfection and orientation: hardness is higher for flawless, pure crystals oriented to the <111> direction (along the longest diagonal of the cubic diamond lattice). Therefore, whereas it might be possible to scratch some diamonds with other materials, such as boron nitride, the hardest diamonds can only be scratched by other diamonds and nanocrystalline diamond aggregates.
The hardness of diamond contributes to its suitability as a gemstone. Because it can only be scratched by other diamonds, it maintains its polish extremely well. Unlike many other gems, it is well-suited to daily wear because of its resistance to scratching—perhaps contributing to its popularity as the preferred gem in engagement or wedding rings, which are often worn every day.
The hardest natural diamonds mostly originate from the Copeton and Bingara fields located in the New England area in New South Wales, Australia. These diamonds are generally small, perfect to semiperfect octahedra, and are used to polish other diamonds.
Golden Jubilee Diamond
The world's largest cut and faceted diamond.
The Golden Jubilee Diamond is the largest cut and faceted diamond in the world. It weighs 545.67 carats (109.13 g). It outweighs the Cullinan I by 15.37 carats (3.07 g). The Golden Jubilee Diamond was discovered in the Premier Mine, which is also the origin of the Cullinan diamond (1905) and other notables such as the Taylor-Burton (1966) and the Centenary (1986). The Cullinan I, also known as the Great Star of Africa, had held the title of the largest cut and faceted diamond since 1908.
The diamond is valued at 4–12 million U.S. dollars.
The Golden Jubilee Diamond was cut from a large brown diamond of 755.5 carats (151 g), found in the prolific blue ground of the Premier Mine in South Africa in 1985. First known as the "Unnamed Brown," the Golden Jubilee was given to Gabriel Tolkowsky by De Beers for the purpose of testing special tools and cutting methods that had been developed for use on the colourless D-colour Centenary.
Because of its deep cracks and several inclusions, the Golden Julilee Diamond was cut in a specially designed underground room free from vibrations. The yellow-brown diamond was transformed through a fire rose cushion cut. Until 1990, the diamond remained largely unknown to the outside world, requiring two years to bring it to its current state.
The unnamed diamond was brought to Thailand by the Thai Diamond Manufacturers Association to be exhibited in the Thai Board of Investment Exhibition in Laem Chabang and was selected to herald De Beer's centennial celebrations in 1988.
The Golden Jubilee was purchased from De Beers by a group led by Henry Ho of Thailand in 1995.
The diamond was brought to Pope John Paul II in the Vatican to receive a Papal blessing. It was also blessed by the Supreme Buddhist Patriarch and the Supreme Imam in Thailand.
The diamond was named by King Bhumibol Adulyadej and given to him in honour of his 50th coronation anniversary. It was initially planned to mount the Golden Jubilee in the royal sceptre. A subsequent plan was to mount it in a royal seal.
The Golden Jubilee Diamond has been exhibited at Henry Ho's 59-story Jewelry Trade Center in Bangkok, the Central Department Store in Lad Prao (Bangkok) Thailand, and internationally in Basel (Switzerland), Borsheims in Omaha, Nebraska, USA (owned by Warren Buffett's Berkshire Hathaway Inc.), and Gleims Jewelers in Palo Alto, California. USA. It is now located in the Royal Thai Palace as part of the Crown jewels.
(source:wikipedia)
