New Zealand Royal Navy Aerial image shows a shelf of white pumice rock floating in the south pacific.

Little-known fact: rocks (some of them, anyway) can float. And a massive one—7,500 square miles, to be specific— is apparently doing just that in the South Pacific.

An odd-looking formation discovered at sea was found to be a large mass of volcanic pumice, a type of lava rock that features millions of tiny air bubbles, which allow it to float on water. Lieutenant Tim Oscar, an Australian officer serving with the New Zealand navy, was in command of the first vessel to make a study of the rock shelf; he told the news site Scoop it was “the weirdest thing I’ve seen in 18 years at sea.”

“The lookout reported a shadow on the ocean ahead of us so I ordered the ship’s spotlight to be trained on the area,” Oscar said. “As far ahead as I could observe was a raft of pumice moving up and down with the swell.”

What Oscar and his fellow sailors had stumbled upon was a piece of pumice apparently created by a massive undersea volcano, bigger than the state of Connecticut. Crews were able to steer the ship into the midst of the pumice to gather samples for research. Pumice, (which is also used as a facial exfoliator), is so light it didn’t pose any danger to the ship. It took about four minutes to travel through the brilliant white sea of stone.

Now the search is on to find the volcano responsible for the monstrous floating pumice shelf.

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