Crown Jewel diamond formed over 400 miles underground
THE CROWN Jewels contain a “super-deep” diamond coming from more than 400 miles below the Earth’s surface and three times deeper than other precious stones, new study reveals.
The analysis showed for the first time that the Crown Jewels’ Cullinan Diamond is one of the rarest objects on the planet, originating hundreds of miles deep inside the Earth.
The largest gem-quality rough diamond ever found, weighing 3,106.75 carats, it was discovered at the Premier No.2 mine, in Cullinan, South Africa, in January 1905.
In 1907, the Transvaal Colony government bought the Cullinan and presented it to King Edward VII who had it cut in Amsterdam, and it is now the centrepiece of the Crown Jewels.
The new study also found that the Hope diamond, at the Smithsonian Museum, in America, may also be “super deep”.
Dr Evan Smith, of the Gemological Institute of America (GIA), said: “We examined the first large gem diamonds confirmed to originate from Earth’s lower mantle, which is several times deeper than most other diamonds. The results support earlier predictions based on smaller gems, suggesting that diamonds with properties similar to those studied, including both the Cullinan and Hope diamonds, are super-deep diamonds.”
Diamonds are formed under high pressure in the Earth’s mantle, the middle layer between the crust and the core. While the majority of diamonds form in the base of the continental tectonic plates, at depths of up to 125 miles, some rare diamonds form deeper in the mantle.
Now Dr Smith and Dr Wuyi Wang, working at the GIA lab in New York, have detected the remains of the mineral bridgmanite in a large diamond.
Dr Smith said: “Finding these remnants of the elusive mineral bridgmanite is significant.
“It’s very common in the deep Earth, at the extreme pressure conditions of the lower mantle, below a depth of 660km (410 miles), even deeper than most super deep diamonds.”
The Cullinan Diamond produced stones of various cuts, the largest of which is named Cullinan I, or the Great Star of Africa, and at 530.4 carats (106.08 g) it is the largest clear cut diamond in the world. The stone is mounted in the head of the Sovereign’s Sceptre with Cross. Another stone is in the Imperial State Crown.