If you look closely,you can find a microscopic star embedded in the wall of the Mosque-Cathedral in Córdoba. Known to some as the Estrella de los Deseos (Wishing Star), this star precisely is located in a corner of the Cathedral-Mosque, or next to Torrijos street. It is actually a type of fossil. People who walk by often touch it and acquire a wish,just in case it will be fulfilled.
Despite the alleged magical properties that have been attributed to it by the ordinary people, the wishing star is just a common fossil typical of the calcarenite stone used in the façade of the building, and which was hidden when the pillar was carved and used to build the wall. The fossil appeared after the lean layer of sandy limestone was degraded. At this moment,the appearance of the fossil would be quickly due its hardest consistency. That must have been a surprise, hence its alleged miraculous power.
The fossil that now can be seen completely is a type of an equinoideo, or the shell of a Clypeaster,a type of marine sea urchin.
Source: atlasobscura.com