Declared as a “once-in-a-lifetime find,” the government-owned Okavango Diamond Company (ODC) in Botswana unveiled an incredibly rare oval-shaped blue diamond weighing 20.46 carats. It’s the largest blue diamond discovery ever made in the nation – and one of the rarest in the world.

The Okavango Blue Diamond was discovered at Orapa mine in Botswana and weighed 41.11 carats of rough stone. The cut diamond is now graded as a Type llb “Fancy Deep Blue” and an Oval Brilliant Cut, one of the highest polished color classifications attainable for any blue diamond, which can only be found at a select few mines around the world.

“From the first moment we saw the diamond, it was clear we had something very special,” said Marcus ter Haar of Okavango Diamond Company in a statement. “Everyone who has viewed the 20-carat polished diamond has marveled at its unique coloration, which many see as unlike any blue stone they have seen before. It is incredibly unusual for a stone of this color and nature to have come from Botswana – a once-in-a-lifetime find, which is about as rare as a star in the Milky Way.”

Its extremely rare blue coloring was created as long as 3 billion years ago during a time of volatile volcanic activity that, when mixed with the mineral boron in the rocks of ancient oceans, produced its vibrant color.

A diamond is made up of carbon atoms that, without impurities, will be colorless. When defects in the diamond crystal show up – like other elements, missing carbon atoms, or particles of mineral matter that don’t belong to diamonds – other colors can turn up. Blue diamonds are caused by trace amounts of the mineral boron that substitute for carbon atoms. These traces be as small as one-part-per-million but the more the boron, the deeper the blue

“It is little surprise blue diamonds are so sought after around the world as only a very small percentage of the world’s diamonds are classified as fancy color and, of those, only a select few can be classified as being Fancy Blue,” said ter Haar.

Undeniably, the world’s most famous is the 45.52 Hope Diamond housed at the National Museum of Natural History in Washington, DC.