Rocks are pretty common around this big chunk of rock we live on, and may not typically be considered unusual. The Maoeraki Boulders are definitely an exception.

Located on Koekohe Beach in New Zealand, these boulders are large, spherical and can weigh up to seven tons (14000 pounds).

What Caused Them?

These boulders are pretty unique. They began to form in sea floor sediments and mud 60 million years ago, and the largest are estimated to have taken over 4 million years to grow to their current massive sizes. They are called concretions, which are big bunches of sediments clumped together by a natural, mineral cement.

The spherical lumps were “glued” together with calcite, likely originating from a rotting animal.

These boulders go by many names including giant gobstoppers, eel pods, hooligan’s ghoul-stones, alien’s brains, and the bowling balls of giants.

By Krzysztof Golik – Own work, CC BY-SA 4.0

Why Are They Round?

Despite a common belief that the ocean water carved perfect spheres into these rocks over time, the actual reason is because they simply formed evenly and uniformly in every direction. The local legends also say that they originated from a canoe wreckage, and are the remains of baskets and food washed ashore. The unique pattern is said to be the remains of fishing nets, though is most likely actually due to a weaker interior and loosely packed calcite.

There are over 50 of these that line the beach today, though only recently came to be there. About 15 million years ago, the boulders were lifted out of the sea in a cliff, and breaking waves have since chipped these 50 off the cliff, rolling down to the beach.

Thousands of tourists visit every year, and since the 1900s a substantial number of the rocks have disappeared. It is believed that people began to take the smaller ones for their collections or gardens, and all Moeraki boulders are now legally protected.