(CNN) A precious gold coin that's in the Guinness Book of Records for its unsurpassed purity was stolen early Monday from a museum in Germany.

The coin, which weighs more than 200 pounds and has a diameter of more than 20 inches, was taken from the Bode Museum in Berlin after 2 a.m. local time. German media reports put the current value of the gold coin at 3.7 million euros, or slightly more than $4 million.

Nicknamed "the "Big Maple Leaf," the coin was issued by the Royal Canadian Mint in 2007, ahead of Queen Elizabeth II's state visit to Germany. It has a face value of more than $1 million and a purity of 999.99/1000 gold.

The coin had been in the Bode Museum collection since 2010.

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