Massive Diamond Weighing 910 Carats Discovered in Lesotho Could Be Worth $40 Million

This 910-carat diamond was discovered in a mine in Lesotho by a British mining company, Gem Diamonds. The company announced its find on January 15. Courtesy of Gem Diamonds

A massive, 910-carat diamond has been discovered in a mine in Lesotho. The company that owns the mine where the diamond was found, Letšeng, announced their find Monday in a press release. The diamond is the largest to come from the mine and is probably the fifth-largest "gem quality" diamond ever found. One analyst told Bloomberg that the stone could be worth up to $40 million.

The quality of a gem, including a diamond, is generally evaluated on four criteria: color, clarity, cut, and carat. Obviously, this stone has that last one covered fairly well; it hasn't yet been cut. The other two components have already been evaluated by the company. According to Gem, this diamond is a D color Type IIa diamond.

What that means is that this particular rock is also remarkably colorless—which is good for a diamond. D is one of the three possible "colorless" grades, according to the Gemological Institute of America (GIA). At the opposite end of the scale, an obviously yellow or brown-ish diamonds might receive a Z color grade.

"Type IIa" indicates exactly what atoms make up the stone. Diamonds are mostly made of up carbon atoms that have been smooshed together at high temperatures, as Smithsonian Magazine noted in one article in a series on diamonds. Once formed, volcanic eruptions brought the diamonds closer to the surface. Where the diamonds eventually settled are known as kimberlite pipes; these pipes are what miners look for today.

However, there can be atoms other than carbon in a diamond, too; for example, there can be nitrogen and boron in the stone's lattice structure. The GIA notes that these odd atoms can also affect a diamond's appearance and chemical properties, including its color and ability to conduct electricity. Type IIa diamonds, however, have only carbon in their lattice.

This diamond is not the largest one ever found, but it's up there. According to, the largest diamond ever mined was over 3,000 carats and was brought to the surface from a mine in South Africa in 1905. The largest cut diamond is the King of Thailand's Golden Jubilee diamond.