It is like something out of a science-fiction film: a huge national park whose ancient native rocks keep sprouting up out of nowhere. But there is nothing science-fiction about the Arouca UNESCO Global Geopark in Portugal, an open-air museum visited by people from all over the world.
The scientific community has long flocked to the park to observe the extremely rare phenomenon, and they are not disappointed. There, they can see first-hand the various “mother stones”, as they have been labelled, rocks that are hundreds of millions of years old, whose surfaces are covered with tiny nodules shaped like discs.
It is these rocks that, quite unexplainably, produce many smaller rocks from somewhere inside them, and so continue the life-cycle of the park’s geology.
The name ‘birthing stones’ — known as Pedras Parideiras in Portuguese — was given to them in the 18th century by Arouca locals. Back then, they had no idea what was happening or how it was happening. It must have seemed like some sort of divine intervention.
Every so often, erosion occurs on the rocks’ granite surface and from this surface are released smaller ‘baby stones’ which leave a cavity from which yet more stones emerge.
High concentrations of precious minerals are found in these stones, including quartz, orthoclase, albite, biotite and muscovite, as well as zircon, apatite, rutile, titanite-leucoesfena, chlorite, microlite and sillimanite.
Experts at the geopark estimate that the rocks and smaller stones inside them were created around 320 to 310 million years ago.
The nodules that fall from the rocks are more resistant to the elements compared to their brothers and sisters found around the world. They withstand extreme winds, rain, heat, frosts, and other natural processes before the rocks inside the nodules are forced out.
While thousands of baby stones can be seen near the surface of the rocks, it’s not exactly known how many more are inside the mother stone. There could be hundreds, thousands, or even hundreds of thousands simply waiting to be “born”.
While similar granite is found around the world, it appears that the physical process of ‘birthing’ is only present at the site in Portugal.
The explanation could lie with Arouca’s position on a fault system and its explosive natural history, though scientists aren’t entirely sure. Given that so much mystery surrounds the process, coupled with its long existence, the Birthing Stones at Arouca have themselves birthed many myths and stories.
Perhaps the most famous is that the rocks harness the power to help couples who are having fertility issues. As Esme Fox explained in a BBC travel piece, the myth goes that if you sleep with one of the baby rocks under your pillow, it will help you conceive a child.
So many people had subscribed to the myth that by the 1990s some birthing stones in and around the park’s present-day boundaries had almost lost all their baby nodules.
“While there obviously isn’t any scientific proof that these stones help couples conceive, it’s curious to note several success stories from those who have obtained these nodules and placed it under their pillows at night,’ said Artur Agostinho de Abreu e Sá, scientific coordinator at the Arouca Geopark.
Today, the park asks visitors not to take or buy the birthing stones from shady vendors, though new schemes in place could help those wanting a bit of fertility luck.
There is, for example, the ‘rent a Pedra Parideria’ programme for those who want to have the stones for a short while but eventually return them.
The stones have become integral to Portugal’s sense of identity and place, a legendary tale that will likely survive the ages and continue in the country’s secretive folklore tradition.
