The Lucara Diamond Company has announced discovering what is believed to be the seventh largest diamond ever found at its Karowe Mine in eastern Botswana, in a press release issued on 8 August 2023. The diamond is described as weighing 1080.1 carats (216.02 g), and to measure 82.2 x 42.8 x 34.2 mm. Importantly, the gemstone is reported to be a Type IIa top white diamond, which is to say a diamond with almost no impurities, a type of diamond which make up only about 1-2% of all diamonds discovered, and which are correspondingly more valuable than other diamonds of similar size.
The largest diamond ever found is the Sergio Diamond, found at Lençóis in Bahia State Brazil, in 1895, by Sérgio Borges de Carvalho, after whom it is named, which weighed 3167 carat (633.4 g). Surprisingly, the Sergio Diamond was not found within a diamond mine, but on the surface. The Sergio Diamond was a carbonado, a type of diamond with a black colour, a micro-porous structure, and a high graphite and amorphous carbon content, as well as frequently containing inclusions of other minerals or metals. Notably, some of the inclusions found in carbonado diamonds are extremely rare on Earth, and they have very low proportions of the isotope carbon¹³ compared to other diamonds, as well as radioactive inclusions, again not found in other diamonds. All caronado diamonds subjected to uranium-lead isotope dating have been found to be about 3 billion years old, and almost all carbonado diamonds come from two locations, Brazil and the Central African Republic. This has led to speculation that these diamonds are derived from an extra-terrestrial body which impacted the Earth in the distant past, although no hypothesis as to how such a body could have formed has ever gained widespread acceptance. Because of their hardness, carbonado diamonds were widely sought for use in drill bits in the nineteenth century, although they have been replaced by more modern materials today. Despite its exceptional size (most carbonado diamonds are smaller than a pea), the Sergio Diamond was sold for £6400 in London in September 1895, then broken up to make diamond drill bits.
The second largest diamond ever discovered, and the largest gemstone-quality diamond, was rhe Cullinan Diamond found at Cullinan in what is now Gauteng Province, South Africa, in April 1905, which weighed 3106 carat (621.2 g) when it was found. The Cullinan Diamond was purchased by Louis Botha, the Prime Minister of the Transvaal Colony, and given to the British King Edward VII, who had it cut into nine large gemstones and a number of smaller fragments known as 'The Brilliants'. The largest of these cut stones, known as Cullinan I or the Star of Africa, has a mass of 530.4 carat, and is mounted on the Sceptre with Cross, part of the British Crown Jewels, which is carried by the monarch at their coronation.
The third largest diamond ever found is the Sewelô Diamond, recovered at Lucara's Karowe Diamond Mine in Botswana in April 2019, which weighs 1758 carats (352 g). This was the largest diamond ever found in Botswana, and its name was chosen by a competition organised by Lucara, meaning 'rare find' in Setswana. The Sewelô Diamond was purchased by the French fashion house Louis Vuitton, with the intention of having it cut into smaller gems.
The fourth largest diamond ever discovered is an unnamed diamond found at Lucara's Karowe Mine in June 2021. This diamond had a mass of 1174.76 carats, and measuring 77 x 55 x 33 mm. This gem is considered to be of variable quality, although with a significant proportion of high quality diamond.
The fifth largest diamond ever discovered was the Lesedi De Rona Diamond, found at the Karowe Mine in November 2015. Like the new diamond, this was a Type IIa top white diamond, and has a mass of 1111 carat (222.2 g) when it was found. At that time, it was the largest diamond ever found in Botswana, and the third largest diamond ever found, prompting Lucara Mining to organise a national competition in Botswana to chose a name. The winning name, Lesedi De Rona, translates as 'Our Light' in Setswana, and was chosen by Thembani Moitlhobogi of Mmadikola. The diamond was purchased by the London-based jeweller Graff, and cut to form one large diamond, the 302.37 carat Graff Lesedi De Rona Diamond, and 66 smaller gemstones.
The sixth largest diamond ever discovered was found at the Debswana-owned Jwaneng Mine in southern Botswana in June 2021, and had a mass of 1098 carat (219.6 g), measuring 73 x 52 x 27 mm.
Thus, the new diamond is the seventh largest diamond ever discovered, the sixth largest gemstone quality diamond ever discovered, the sixth largest diamond ever found in Africa, the fifth largest diamond ever found in Botswana, the fourth largest diamond extracted from the Karowe Mine, and one of only seven diamonds ever found with a mass of greater than 1000 carat.
That five of these seven diamonds have been found in Botswana, and four of them from a single mine, since 2015 is not a coincidence. but marks the introduction of new technology pioneered at the Karowe Mine. Modern mines typically use crushing machinery to extract diamonds from their parent rock, but this is generally thought to break up a significant proportion of larger diamonds. The Karowe Mine uses X-ray fluorescence technology to scan ore before it passes into the crushing equipment, thus allowing for the machinery to be stopped and particularly large diamonds to be recovered.
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