Crown Jewels that began life 400 miles underground
THOUSANDS of precious stones make up the Crown Jewels but no one has been aware of just how special they are – until now.
A study found that the centrepiece diamonds in the collection were formed 400 miles below the Earth’s surface.
The Cullinan – the largest gem-quality rough diamond ever found, weighing 3,106 carats or 1.3lb – was made at depths three times deeper than most other precious stones.
It was discovered at the Premier mine near Pretoria, South Africa, in 1905 and was cut into several gemstones. The largest, known as the Great Star of Africa, features in the Sovereign’s Sceptre and another is in the Imperial State Crown, pictured.
And both the Cullinan and another giant gem – the Hope diamond which is found at the Smithsonian museum in the US – were formed far deeper than typical gemstones sold in jewellery shops. Researchers studied a 124 carat diamond from a mine in Lesotho, South Africa, and found it had remnants of a mineral called bridgmanite.
This mineral is only found 400 miles underground meaning that the gem must have come from deep in the Earth’s mantle – the middle layer between the surface crust and the central core. In comparison, most diamonds are formed higher in the mantle at depths of only 125 miles.
The researchers found that the Lesotho diamond shares similar properties with the Cullinan and Hope gems, such as their size and purity, which suggests that they all had similar origins deep in the mantle.
Researcher Dr Evan Smith, of the Gemological Institute of America (GIA), said: ‘The results suggest that diamonds with properties similar to those studied, including both the Cullinan and Hope diamonds, are super-deep diamonds.’
These diamonds are formed from metallic liquid and shoot to the surface during volcanic eruptions.