"Diamonds", sang Marilyn Monroe in the film Gentlemen Prefer Blondes, "are a girl’ s best friend." You might not agree, but you

"Diamonds", sang Marilyn Monroe in the film Gentlemen Prefer Blondes, "are a girl’ s best friend." You might not agree, but you can be sure that diamonds are not only the hardest substance in the world, they are also the most expensive.A single diamond sold for $16.5 million at an auction in Geneva in 1995!
      Diamonds are found in a number of countries including Australia, South Africa, Brazil and the Russian Federation.In fact, there are two main types of diamonds.These are colourless diamonds （about 25% of those found）, which have only a few impurities and are usually made into jewellery, and black diamonds—the remaining 75%—which contain a lot of impurities, and are used in industrial applications.Industrial diamonds arc also produced artificially.
      The largest diamond ever found is the Cullinan diamond.It weighed 620 grams and was found in a South African diamond mine in 1905.It was bought by the Transvaal Government for ￡150,000, and then presented to the King of England, Edward VII.The diamond was then cut into nine smaller jewels, which are now part of the British crown jewels.These jewels belong to the British government and are kept in the Tower of London.