Black carbonado diamonds are among the rarest gems on Earth, and a 555-carat specimen going to auction in February is especially noteworthy. As the Associated Press reports, "The Enigma" diamond is purported to be from outer space, though some experts are questioning its origin story.
Sotheby's expects to sell the stunning jewel for at least £5 million, or $6.8 million USD, at its London auction house next month. The Enigma will go on a press tour before hitting the auction block, making stops in Dubai and Los Angeles.
The shape of the diamond is modeled after the Khamsa, a Middle Eastern symbol of strength and protection that means five in Arabic. The theme of five is reflected in the stone's 55 facets and its weight of 555.55 carats.
Carbonado diamonds are found in Brazil and the Central African Republic, but some originate from much farther away. A press release from Sotheby's [PDF] states that The Enigma is "thought to have been created either from a meteoric impact or having actually emerged from a diamond-bearing asteroid that collided with Earth."
The equatorial countries of Brazil and the Central African Republic were once part of Rodinia, a supercontinent believed to have been battered by meteorites millions of years ago. Sotheby's cites this as evidence of the carbonado diamond's interstellar origins.
While some black diamonds do come from space, they also could have formed on Earth. Carbonado diamonds from meteorites are usually much smaller than The Enigma, which has led some geology experts to question Sotheby's claims. And without pictures showing the outside of the gem before it was cut, it's impossible to confirm its background.
Whether it's an earthling or an extraterrestrial, the diamond likely won't have trouble attracting high bidders next month. Its unique color and impressive size have already generated international attention, and its mysterious nature only adds to its intrigue.