In order to learn more about this undoubtedly special phenomenon, I spoke with scientist, Alexandra Paz from the “Casa das Pedras Parideiras” Interpretation Centre at Arouca Geopark.
To lay the scene, the municipality of Arouca has been classified as a UNESCO Global Geopark since 2009 and the Interpretation Centre opened in 2012. This Geopark has 41 listed geosites in its territory of which are of geological interest, with just one of them being Arouca Geopark where you can find the Interpretation Centre and can learn all about the unique phenomenon of ‘Pedras Parideiras’ which translates to ‘Birthing Stones’.
I learnt from Alexandra that the name ‘Birthing Stones’ was the name given to the stones by the local inhabitants of Arouca and that it began to be written down as early as the 18th Century.
However, the stones are geologically cited as the nodular granite of Castanheira, with the rocks extending through a terrain of 1000 meters by 600 metres.
It was incredible to see a Birthing stone, I didn’t know what to expect, but I didn’t expect a flat-shaped rock, which was almost disk-like. I was told they vary between 1- and 12-centimetres in diameter. Alexandra explained that as the granite “mother rock” erodes, the nodules “baby stones” are released from the rock leaving a cavity in the granite, which is why it is described as a “rock that delivers a stone”. The granite has concentrated sections of minerals, which are quartz, orthoclase, albite, biotite and muscovite as well as accessory minerals zircon, apatite, rutile, titanite-leucoesfena, chlorite, ficrolite and sillimanite.
The main purpose of the Casa das Pedras Parideiras is for the conservation and valorisation of the geosite. It is an unusual interpretation centre, with Alexandra branding it “out of the box”, because the areas where the rocks are observed are the outer areas in which it is possible to circulate freely. “We invite everyone to take a guided tour, where we explain the science behind these rocks, you can walk around unguided but we do not recommend this because you will lose specific details and why it is such an important rock. The guided tours, pass by the auditorium, where we also have an informative 3D documentary called “Pedras Parideiras: a geological treasure.”
Only one in the world?
Alexandra confirmed that this Birthing stone can only be found in Arouca, despite the internet suggesting that there is this stone elsewhere. Alexandra affirmed that: “Up until now there is no concrete evidence that there is an identical phenomenon, there are references which we have scientifically and geologically verified that are not identical to the Birthing rocks specificity.”
“Granite is common and sometimes there are similarities in other rocks but they are not identical with the specificity of these minerals in the granite and that this is the only one we know of right now, it would be more conclusive if we had another of the same rock to compare to from a scientific point of view, everything that is unique leaves us with a question mark.”
When asked what happened to form the granite, Alexandra replied that “We don’t know the process that caused this to happen, mostly the dark shade of the rock is not dispersed but concentrated in one area, they are abnormal concentrations but when we cut the rock in half, in the middle, we can see the minerals, it is incredible to think that this rock formed inside the earth. Very specific conditions were needed to create this rock, with the geological characteristics which we can only find in Arouca.”
The Birthing Stones Myth
Alexandra told The Portugal News that the words magic and mysticism are what come to mind, when you think of the ‘Birthing Stones’. Alexandra explained that the Birthing stones are believed by some people to hold “baby-making powers, and that by putting one under your pillow, you will increase your chance of fertility, which is why these stones were so sought after and often taken home.”
This strong cultural tie to the stone remains, however, the Centre now has a loan system, so you can take a birthing stone home and bring it back. Alexandra even told The Portugal News that “In the past 10 years there have been people who have told the Centre that it has worked for them. The loan system works well for us because often people believe they can just find the nodules outside our Centre but they are difficult to actually find and we want to preserve them as much as possible when we do find them.”
“There are lots of people who in this area have the nodules at home, because there was no limitation of how many they could keep as well as in the surrounding councils and there was a lot of curiosity tied to it.” People often say “I have one at home but it doesn’t produce more stones” but the rocks are not alive and continuously birthing ‘stones’, despite its name, it is not multiplying like many people originally thought.”
The Future of the Interpretative Centre
Alexandra explained that “Casa das Pedras Parideiras” Interpretative Centre is starting to lack in space, especially when you consider how many people visit. An incredible 30,000 visitors from all over the world visit the Centre, with 6,000 being school visits that come to understand this geological phenomenon that is very present in school curriculums. Expansion is definitely on the cards for this centre including a larger auditorium and laboratory.
For more information about Birthing Stones, please visit the Interpretative Centre at Arouca Geopark, which is open every day from 9:30am until 12:30pm and from 2pm until 5pm.