Rocks of the Ages is the "skill" used in finding the various types of granite and marble in Egypt. Although it is learned at a School of Architecture and has a tuition cost (10 slate), it is different from normal skills in a number of ways:
There are many varieties of marble in the game (see Granite and Marble for a full list). When you learn Rocks of the Ages, you specify one type of marble to which you will be attuned. You can return to a SArch at any time and change your attunement by paying another 10 slate.
Depending on the marble chosen, you will need a certain minimum Perception to attune yourself to it:
It is perfectly fine to learn the skill with a temporarily boosted Perception (e.g. through food), and you will stay attuned to your marble even after the boost wears off. However, you will have to boost your Perception again later in order to actually use the skill to prospect.
Rocks of the Ages allows you to prospect for the type of marble to which you are attuned. You will need a partner as well as a good supply of slate. For more detail, see the Quarrying guide.