Geoturism Balearic Islands

In the highest part of the rocks called radiolarites, which will be described in Stopping Point 6, it is frequent to find nodule masses. In other words, rounded mineral masses that are inside other rocks (in this case, the radiolarites) and that are different from them. The composition of the nodules that we can identify at this stopping point is phosphate, and their presence is related to times when there is no sedimentation.

In the Earth’s crust, we usually only differentiate carbonate rocks from silicate ones. This discrimination is logical considering the great predominance of these rocks; however, occasionally we find other compositions, as is the case of phosphate.

These rocks are formed in anaerobic conditions on the seabed. The phosphate comes primarily from tissues of organisms, which consume oxygen when degrading, giving rise to an atmosphere poor in this element. This way, in places with a high organic matter content, and at a depth of between 60 and 300 metres, the phosphate can precipitate around a nucleus such as a fossil or any small cobble, leading to these concretion nodules. For this process to be effective, sedimentary stoppage of other components that do not affect the precipitation is essential.

Next to the tectonic, eustatic or antropical processes</span></p></div>">outcrop featured in the stopping point, right by the sea next to the cliff, and being very careful not to fall, it is worth looking at a superb Sedimentary rock composed fundamentally of radiolaria, single-cell organisms usually with a siliceous shell.</p></div>">radiolarite fold.