Diamond is the hardest material known to man and one of the two best known forms (or allotropes) of carbon, whose hardness and high dispersion of light make it useful for industrial applications and jewelry. Diamonds are specifically renowned as a mineral with superlative physical qualities — they make excellent abrasives because they can be scratched only by other diamonds, About 130 million carats (26,000 kg) are mined annually, with a total value of nearly USD $9 billion. About 100,000 kg are synthesized annually.The name “diamond” derives from the ancient Greek adamas (“invincible”). They have been treasured as gemstones since their use as religious icons in India at least 2,500 years ago—and usage in drill bits and engraving tools also dates to early human history. Popularity of diamonds has risen since the 19th century because of increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns.Roughly 49% of diamonds originate from central and southern Africa, although significant sources of the mineral have been discovered in Canada, India, Russia, Brazil, and Australia. They are generally mined from volcanic pipes, which are deep in the Earth where the high pressure and temperature enables the formation of the crystals.

Facts about diamonds Research indicates:
• In 2004 £1.2 billion worth of diamond jewellery was sold in the UK.
• That in 2004 some four million pieces of diamond jewellery were sold at an average price of approximately £300
• The UK diamond jewellery market has grown steadily for the past ten years (1994 – 2004).
• The UK is the second largest market in Europe for diamond jewellery. Italy is the largest.

Did you know?
• All diamonds are immensely old and were formed long before dinosaurs roamed the earth. The youngest diamond is 900 million years old and the oldest is 3.2 billion years old.
• Every diamond is unique; no two are alike.
• Diamonds exist in many colours not simply ‘white’.
• The most rare diamonds are red.
• Each diamond loses, on average, more than half its original weight during the cutting and polishing process.
• The word ‘carat’ – in measurement used to describe the size of the diamond – comes from the carob tree, whose seed was used as the standard in weighing precious stones.
• Less than 5% of all the diamonds made into jewellery are larger than one carat.

Source: http://www.diamond-heaven.co.uk/about-diamonds.php