Why is this Rock on the Wall?

There could be multiple reasons as to why this specific piece of rock is on the wall. The reason I have come to find is that a while back the original pope residence was torn down and remodeled. This piece of rock was taken from the old residence out of the Clementine Hall, which is where it gets its name from. It was brought here by a reporter who was there to cover the story of the remodeling of the building. I am not sure if there is still a Clementine Hall in the new residence, but it will sure be remembered from the old residence.