A world-class collection of 296 naturally coloured diamonds is on display at the Natural History Museum. They are on loan to the Museum by diamond collectors Alan Bronstein and Harry Rodman.

The Aurora Pyramid of Hope has 267.45 carats of exceptionally rare stones, from the 12 colour varieties, and reveals an enchanting spectrum from emerald green to blood red.

'Gems like these were not meant to be imprisoned in a dark vault for the momentary pleasure of a few eyes,' said Alan Bronstein, co-owner of the Aurora Pyramid of Hope. It's thrilling to think that the collection will be seen by the 3.6 million visitors that come to the Natural History Museum each year.'

Rarity of colour

Coloured, or so-called 'fancy' diamonds, are very rare and are more desirable than ever - coloured stones were recently worn by actresses Halle Berry and Scarlett Johansson to glamorous Hollywood events.

Only one in every 10,000 gem-quality diamonds is coloured. Normal, clear diamonds are made of carbon, but coloured diamonds can occur when tiny amounts of other elements are present or if there are atomic-scale defects in the diamond's structure.

'Each coloured diamond tells its own story, giving us insight not only into its formation but also to the deep Earth processes that took place when the gem was formed,' says Alan Hart, minerals expert at the Museum.

'For example, yellow diamonds are due to the presence of nitrogen in the structure, and green diamonds owe their colour to natural radiation damage. It's an amazing opportunity to be able to display this unique collection of exceptionally rare gems at the Museum.'

Glowing diamonds

The Aurora Pyramid of Hope highlights a little-known property shared by coloured and white diamonds - some of them glow and change colour when exposed to ultraviolet light.

This stunning collection of diamonds is now on display at the end of the Museum's Minerals and Meteorites gallery, and made its European debut in the Museum's Diamonds exhibition in 2005.