With the recent discovery of a 391-carat Type IIa diamond at the Meya Mine in Sierra Leone, the tiny West African nation can now claim to be the source of six of the world's most exceptional rough diamonds.

Officially, the still-unnamed stone will slot in at #54 on Wikipedia's "Largest Rough Diamonds" list, joining the Star of Sierra Leone (10th, 1973, 968.9 carats), The Woyie River (17th, 1945, 770 carats), Peace Diamond (21st, 2017, 709 carats), The Sefadu (24th, 1970, 620 carats) and Meya Prosperity (40th, 2017, 476.7 carats).

As we learned recently with the unveiling of the 2,492-carat diamond from the Karowe Mine in Botswana, the key to sourcing "mega-diamonds" is getting them through the sorting process intact.

In the case of the recent Meya find, mining officials reported that the 391.45-carat stone would have weighed 514.99 carats if it hadn't broken into three pieces. The other two chunks weighed 105.43 carats, and 18.11 carats, respectively.

Back in 2017, the 476.7-carat Meya Prosperity was part of a larger stone that met the same fate. That rough gem weighed 523.44 carats and also fractured into three pieces. The primary chunk was purchased by luxury jeweler Graff for $16.5 million.

"Our priority now is to ensure that going forward we can recover these high-value stones intact," said Jan Joubert, CEO of Meya Mining. "We will work closely with our engineering and processing partners to upgrade the plant, eliminate breakages and increase its capacity to recover exceptionally large diamonds."

Joubert emphasized that only four mines in the world "infrequently" recover these exceptional, high-quality, +500-carat diamonds.

Said Joubert, "The fact that Meya has recovered two +500-carat Type IIa diamonds after treating only 84,195 tons of competent kimberlite from the Meya River domain suggests that there is a high probability of recovering more and possibly bigger diamonds once the mine reaches steady state production of 500,000 tons of kimberlite throughput per annum."

The Type IIa classification represents a colorless diamond with no measurable impurities. Type IIa gems account for less than 2% of all natural diamonds.

The Meya Mining concession encompasses 80 square miles located within the diamond-rich Kono District.

Credit: Sierra Leone's minister of mines and mineral resources Julius Daniel Mattai shows off the 391.45-carat diamond. Photo courtesy of Sierra Leone's National Minerals Agency.