This amazing phenomenon of nature has been observed in many different parts of the world. But no one can explain its cause clearly yet.
We are talking about the so-called boulders of Moeraki, also known as the "watermelons of Elijah the prophet. Someone takes them for the eggs of dinosaurs, someone - for the fruit of ancient marine plants, and some even put forward the assumption that they are the remains of UFOs.
The phenomenon is really strange. Imagine an almost perfectly shaped stone or iron ball with a diameter of ten centimeters to three meters.
If someone happens to meet such an "egg" split open, inside he will find a cavity with crystalline formations on the inner surface.
The most famous collection of such eggs is located in a fishing village in New Zealand. The balls lie directly on the beach. The structure of the stones varies, though; some are smooth, while others are rough, like a tortoise shell. Some are split into pieces or have huge cracks.
But to admire the "watermelons of Elijah the Prophet," you don't have to go to New Zealand. They can be found in China and in Israel. The same round stones can be found in Costa Rica, where they are called "balls of the gods. These stones are considered to be man-made, they are called "the eighth wonder of the world" and they are under the protection of the state.
The largest "balls of gods" in Costa Rica are up to three meters in diameter and weigh about 16 tons. And the smallest - no bigger than a child's ball, have only ten centimeters across. The balls are arranged singly or in groups of three to fifty pieces, sometimes forming geometric shapes.
There are similar formations in Russia (although Russian "eggs" are not considered man-made). For example, mysterious stone balls were found in the village Boguchanka, in the north of the Irkutsk region. Locals are convinced that these are UFOs because the balls look as if they were made of metal.
Where did this "wonder of the world" come from? The assumption that the stone balls - the eggs of dinosaurs, scientists reject immediately for the reason that even the largest dinosaurs could not have such huge calves. The appearance of some stone balls can be explained by the impact of glaciers.
And as for the "iron UFOs" and hollow boulders inside, the official science considered that it is a geological formation, and even gave it its name - a jodan - a closed cavity in any sedimentary or volcanic rocks. But all this is only speculation. Most of these formations are at least 60 million years old, according to researchers' estimates.