Why were these rocks selected
They used granite because it is a hard and though rock that resist erosion, and it was very used in Madrid at that age.
They used limestone because it was (and it is) very used in that time because it is easy to recognise, but is less hard comparating it with cooper
Alterations sufered
The alterations granite sufferes are because of living microorganisms, pollution (carbon dioxide), and meteorological phenomena such as rain(granite is not very resistant to watter), wind … etc. They cause the rock to become darker and to turn red.
limestone sufers alterations when is in contact with acid (for example hydrolic acid), it can be diluated by watter with the pass of time, and this causes the rock to be dissolve in watter.
Comparative
If we compared the materials used in the Palacio de abrantes, we can see that it has granite in the columns of the door and limestone.