Imagine the engagement ring.

An Australian mining firm said Monday that it found the largest diamond ever to be dug up in the southern African nation of Angola. The gemstone weighs a whopping 404.2 carats.

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Lucapa Diamond Company, which discovered the 7-centimeter-long diamond in the northeastern Angolan province of Lunda Norte, said the diamond is the biggest ever to be recovered by an Australian company. The 2.75-inch jewel is about the length of a credit card.

“We’re not used to valuing 400-carat diamonds,” Miles Kennedy, Lucapa’s chairman told the Australian Broadcasting Corporation, “but if we look at other diamonds slightly less weight than this, you’re looking in the order of $20 million.”

The diamond is the world’s 27th largest, according to Lucapa, citing data available on Wikipedia. The previous record-setter for largest diamond discovered in Angola—the so-called Angolan Star—is almost half as massive at 217.4 carats. Last November, a different mining company, Lucara, recovered a 1,111 carat diamond in Botswana.

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Lucapa, based in West Perth, owns a 40% stake in Lulo, the mining project responsible for the find. Angola’s national diamond company Endiama owns 32% stake and a private local firm Rosas y Pétalas owns 28% stake in the project.

Mining operations began at the site last year. Kennedy told ABC that he plans to sell the diamond to fund an expansion in the area.