The world's largest ever diamond exhibition has opened its doors at the Natural History Museum. Alice Eaton got a sneak preview of some of the impressive gems on display.

FROM the ancient Romans who wore them to protect against madness and mortal fear, to the glamorous Marilyn Monroe singing their merits in Gentlemen Prefer Blondes, diamonds have long held a fascination for us.

And now diamond-lovers can get their fill of the precious stone at a brand new exhibition being held at the Natural History Museum, where the finest diamonds from around the globe have been brought together to create a truly dazzling display.

The exhibition is not just about gawping at the kind of rocks you normally wouldn't get within grabbing distance of, although there is certainly plenty on display that is sure to set women's fingers twitching and have men holding on protectively to their wallets and looking about for the nearest exit.

As well as the extensive array of ice on show, visitors can learn how diamonds are formed, the role they have played throughout history and the measures in place today to prevent the flow of conflict diamonds - the rough diamonds used by rebel movements to finance wars against legitimate governments.

Video monitors, interactive presentations, theatrical lighting and an atmospheric soundtrack all help to set the right mood and bring the subject matter to life.

So what makes diamonds so special? As the exhibition explains, it is their rarity which distinguishes diamonds apart from other precious stones.

Diamonds formed billions of years ago deep within the earth under intense heat and pressure. Incredibly, the youngest diamond is 900 million years old. It takes an extremely rare kind of volcanic activity to bring them to the surface and, although their rarity means all diamonds are valuable, only about 20 per cent of those mined are of gem quality.

The rest are used for a variety of industrial purposes. Due to its extreme hardness, resistance to wear and remarkable electrical, optical, thermal and chemical properties, diamonds make the ultimate engineering material.

Until recently, the high cost of using natural diamonds has made it impossible to fully exploit its properties but now, with the creation of a synthetic diamond, its full potential has been unleashed.

The synthetic diamond is beginning to play a part in many areas of our lives, from precision hi-fis to nail polish. Potentially life-changing applications in electronics, communications and medicine are being developed: diamond transplants can be fitted into failing eyes and, one day, diamond nano-machines may even patrol your body, monitoring your health.

But it is the diamond's sheer beauty as a fashion accessory that makes it the most coveted gem for men and women throughout the world. The exhibition has brought together an impressive collection of diamond jewellery, lent by private collectors, companies such as De Beers and Cartier, other museums and even Her Majesty the Queen, as well as key pieces from the NHM's own collection.

The display illustrates how fashions have changed throughout the centuries, from the simple design of a third-century Roman ring through to the cube-shaped ring worn by celebrity Sharon Osbourne.

Other highlights include the Fred Leighton Edwardian tiara worn by Catherine Zeta-Jones at her wedding to Michael Douglas, the revealing Spiderman dress worn by Samantha Mumba to steal the limelight at the premiere of Spiderman II and the obligatory touch of bling provided by R&B star Usher's watch which features his face in coloured diamonds.

However, the real treasures of the exhibition are housed in its 'VIP lounge' where all the A-list gems are on display. It contains some of the finest examples of coloured diamonds - the rarest and most valuable form of the precious stone.

Just to give you an idea of how special these gems are, there are only six known truly red diamonds in the world. The highest price ever paid for such a gem was $1,250,000 for a six-millimetre purplish-red that was badly flawed and less than one carat.

Among the star line-up in the VIP lounge is The Steinmetz Pink, the world's largest vivid pink, flawless diamond, loaned to the NHM by Steinmetz, main sponsor of the exhibition. It took Steinmetz almost two years to cut this magnificent 59.60-carat, oval-shaped diamond which was first revealed around the neck of model Helena Christensen in Monaco in 2003.

Another magnificent example on display is The Ocean Dream, one of the largest naturally occurring deep blue-green diamonds at 5.51 carat. Its incredible colour was caused by exposure to natural radiation over millions of years deep in the earth and makes it one of the world's rarest diamonds.

However, The De Beers Millennium Star diamond, most famously the subject of a failed robbery attempt by thieves when on display at the Millennium Dome five years ago, is certainly the jewel in the crown of the exhibition.

The flawless 230-carat diamond, plucked from river gravel diggings in the Congo, takes pride of place in a glass display box in the lounge where it continuously rotates, casting its dazzling brilliance in shafts of bright light against the surrounding walls. It is truly breathtaking.

This really is the queen of diamonds, although unfortunately a little too large to have set into a ring - even if you could afford it.

  • Diamonds runs at the Natural History Museum until February 26, 2006. For more information, call 020 7942 5000 or visit www.nhm.ac.uk.