Theories of extraterrestrial monuments, dinosaur eggs, and relics of an ancient civilization have been surrounding these strange Siberian geological quirks, but scientists are homing in on what's behind these strange "Jurrasic pearls". 

The 10 gray globes of rock were unearthed around 30 meters (100 feet) deep in the Sereulsky coal mine, in the Nazarovo district of Russia’s Krasnoyarsk region. As if they weren’t alien enough, they also turn to a rusty brown color when it rains due to iron oxide present within them.

The Siberian Times reports that local scientists have already moved in, in an attempt to identify these oddities. No surprises, they were formed through a completely natural process over the course of millions of years. It’s believed that they are a thing called a “concretion” – a hard sedimentary body of mineral matter that has formed layers around a central nucleus, such as a piece of rock or organic debris.  

Since being dug up, the globes have been placed along the side of the roads at the coal mine in an impromptu display.

Olga Yakunina, of the Geology Museum of Central Siberia, told the Siberian Times: “The balls are formed the same way as a pearl, when a grain of sand gets into the shell and the clam tries to get rid of it. Water flowing through sedimentary rock leaves behind minerals that glue together masses of sand, mud or other particles. These concretions are very rare.”

This is far from the only the instance of this geological phenomena. Concretions can be found across the natural world, including the Moeraki Boulders in New Zealand, the golf ball-sized “Moqui marbles” of Utah, and even on the surface of Mars.