### Moeraki Boulders (Kaihinaki)
New Zealand — Looking exactly like giant, hatched alien eggs scattered on a beach, these massive stone spheres are entirely natural.
According to local Māori legend, these giant stone spheres are petrified eel baskets and water gourds washed ashore from the wreck of an ancient sailing canoe. It is easy to see why people thought they were manufactured—they look way too perfectly round to be natural. But they aren't carved, and they didn't fall from space. They grew.
Around 60 million years ago, this beach was a muddy ocean floor. Down in the muck, minerals like calcium carbonate began cementing loose sediment together around tiny pieces of shell or bone, creating a rock called a septarian concretion. Because the minerals spread outward in all directions at the exact same rate—a process called mass diffusion—the rock grew into a perfect, massive sphere.
It took up to 5.5 million years for the largest boulders to slowly form in the mud. Later, the spheres fractured internally, and spectacular yellow and brown calcite crystals grew in the empty cracks. Finally, the ocean eroded the coastal cliffs, dropping these massive, crystal-filled "eggs" right onto the beach for us to find.