Dream on, Jerry: This yellow sun-drop diamond, on display in London, is so rare that it really is... PRICELESS

The Cora Sun-Drop is among the most stunning diamonds in the world, so rare that it is almost impossibe to determine its value. Which is why no-one has even tried.

No wonder model Jerry Hall was bedazzled by the gem today as it arrived at London's Natural History Museum where it is to be displayed in The Vault.

At 110-carats, the Cora Sun-Drop is roughly the size of a woman's thumb and is largest vivid yellow pear-shaped diamond known in the world.

The yellow Cora Sun-Drop pear-shaped diamond is so rare that no-one has even tried to put a value on it

It has been lent to the museum by leading US diamond manufacturer Cora International for display to visitors for a limited time from tomorrow.

Its unusual yellow colour stems from the very small percentage of nitrogen within the carbon structure of the stone.

Diamonds with a strong saturated colour represent only a tiny percentage of all natural diamonds, and when it more than 100 carats, it takes on a historic significance as so few exist.

Model Jerry Hall is dazzled by the 110-carat diamond as it is unveiled to the world at London's Natural History Museum today

The diamond will be in good company. The Vault is a permanent gallery at the Natural History Museum dedicated to some of mother nature's most rare, unique and valuable treasures through its collection of the finest gems, crystals, metals and meteorites from around the world.

These include the Devonshire Emerald, the Aurora Pyramid of Hope - a world-class collection of 296 naturally coloured diamonds - Heron-Allen's cursed amethyst and the Nakhla, an extremely rare Martian meteorite.

Alan Hart, the Natural History Museum's minerals curator, told BBC News: 'I've never seen a stone such as this.

Only a tiny percentage of the world's diamonds have such a strong saturated colour, and Jerry seems to think it would be a perfect fit for her engagement finger

'A one-carat diamond is what most people are familiar with, and are really pleased to own. You can see how exceptional this diamond is.'

For more than 30 years, Cora International has been a leading supplier for all qualities of white and fancy coloured diamonds and has cut some of the most sought-after stones in the world.

Jerry obviously has her eye on the diamond, and clearly shows what an enormous stone it is