910 Carats! African Diamond Is Fifth Largest Ever

This 910-carat diamond was discovered in a mine in Lesotho, in southern Africa. (Image credit: Gem Diamonds Limited)

It sounds like the start of a James Bond feature: A 910-carat diamond has been discovered in a mine in the African country of Lesotho. The find is the fifth-largest gem-quality diamond ever discovered.

Gem Diamonds Limited, a mining company that operates in Lesotho and Botswana, announced the find yesterday (Jan. 15). It's the largest diamond ever found in the country's Letšeng mine, which has a reputation for turning up monster rocks. In 2006, a 603-carat diamond dubbed the "Lesotho Promise" was found at the same mine.

A 910-carat diamond weighs 6.4 ounces (182 grams), said Philipp Heck, a curator in the Earth sciences section of Chicago's Field Museum of Natural History who was not involved in the gem's discovery.

"It's definitely a big deal," Heck wrote in an email to Live Science. "This is a very large and rare diamond." [Sinister Sparkle Gallery: 13 Mysterious & Cursed Gemstones]

Making the find even more exciting is that it is of a quality coveted by jewelers and jewelry-lovers. The diamond is a Type IIa diamond, a category of diamond very low in nitrogen: For every million carbon atoms in a Type IIa stone, there are fewer than 10 nitrogen atoms, Heck said. Nitrogen lends diamonds a yellow hue, so the low concentrations of the element in the new Lesotho find mean the diamond is quite colorless.

Letšeng mine has a high concentration of diamonds, Heck said, but most are small. The sheer number, though, means that a few giants lurk in the mine, too.

Diamonds are formed about 125 miles (200 kilometers) below the surface of the Earth, where pressure and heat squeeze carbon molecules into a very strong crystalline structure. This requires temperatures of around 2,200 degrees Fahrenheit (1,200 degrees Celsius) and pressures upward of 725,000 pounds per square inch. To remain diamonds, these crystals must be brought to the shallow surface within a matter of hours by deep volcanic eruptions, allowing the objects to cool rapidly, locking their crystalline structure in place.

The monster rock from Letšeng is still raw and uncut, but will likely be faceted and polished to give it the sparkle that diamond buyers love so much, Heck said. Diamonds as large as the newly discovered stone rarely get divided into smaller stones and sold at places like Zales, he said; they're more likely to be kept ridiculously giant and sold at auction to well-heeled bidders.

Don't worry too much about that Bond plot, though. Diamonds are used in the internal workings of lasers, but a dastardly villain would have better luck using a synthetic diamond in a world-destroying weapon, Heck said.

"Even this new, big and clear Lesotho diamond is probably less pure and therefore less suitable for a laser than a synthetic diamond," he said.

Original article on Live Science.

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Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor's degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.