10. Incomparable Diamond
> Weight: 890 carats (6.3 oz)
> Mine found: MIBA Diamond Mine, Democratic Republic of the Congo
> When: 1989
Some diamonds are found by accident. In 1989, a girl looking through the mine tailings of the MIBA Diamond Mine in the Democratic Republic of the Congo noticed a deep brownish yellow diamond weighing 890 carats. It took four years for experts in Antwerp, Belgium, to analyze and finally cut the diamond. Cut into a triangular drop weighing 407.38 carats, it was named The Incomparable. In 2013, Mouawad Jewelers set it into a 367-carat diamond necklace that is listed in the Guinness World Records as the world’s most expensive necklace, worth $55 million.
9. Lesotho Legend
> Weight: 910 carats (6.4 oz)
> Mine found: Letseng Mine, Lesotho
> When: 2018
The 910-carat Lesotho Legend was discovered by Gem Diamonds at the Letseng Mine, another diamond mine famous for the size and quality of its diamonds, particularly white diamonds. The mine is one of the highest in the world at 10,000 feet above sea level. The rough diamond sold for $40 million to an unnamed customer in March 2018 but no cut gems have yet been unveiled. Gem Diamonds says it is the largest diamond to have been recovered from the Letseng Mine.
8. Star of Sierra Leone
> Weight: 969 carats (6.8 oz)
> Mine found: Diminco, Sierra Leone
> When: 1972
The Star of Sierra Leone was found on Valentine’s Day in a river near Koidu in Sierra Leone in 1972. It was purchased by Harry Winston and brought to New York. It was initially cut into a 143.20-carat emerald cut but because of a flaw, it was recut into a 42-carat pear shape by New York firm Lazare Kaplan. Another 17 diamonds were produced from the rough stone and six of them were set into a brooch. The Star of Sierra Leone is the largest alluvial diamond ever found; every larger gem has been recovered from a primary deposit. It is likely worth more than $6 million. The famed 770-carat Woyie River diamond also was found near Koidu, in 1945.
7. Excelsior Diamond
> Weight: 995 carats (7.0 oz)
> Mine found: Jagersfontein Mine, South Africa
> When: 1893
When the 995-carat rough Excelsior Diamond was discovered, it was the largest diamond ever found to that point. It was so large and flawless, no one initially wanted to buy it. It was cut into many small diamonds in 1904 by renowned diamond cutter Joseph Asscher of Amsterdam. The largest of them is a pear-shaped gem weighing 69.69 carats and worth more than $10 million.
6. Unnamed diamond
> Weight: 998 carats (7.0 oz)
> Mine found: Karowe Mine, Botswana
> When: 2020
A 998-carat rough diamond was discovered in Botswana at the Karowe Mine. It is the latest find made using equipment and technology designed specifically to unearth exceptionally large diamonds. The unnamed gem might be worth $50 million or more, based on the per-carat price fetched by diamonds with similar characteristics. The 998-carat stone was the second 500-plus carat diamond recovered from the mine in 2020. Karowe produced 31 diamonds greater than 100 carats in 2020. The mine’s owner, Lucara, is working with diamond cutting and polishing specialist HB Antwerp to evaluate the next steps in maximizing the value of the rare large stone.
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