[Prime Choice]

You are suggesting it is probably just a shadow then? I do agree, on closer inspection it is not exactly rectangular on the top.

A shadow most likely, with a remote possibility that it's a different rock type embedded in the larger rock. Won't be able to tell until we get a picture at a different time of day to rule out a shadow.

[Orion78]

Agreed, a picture from a different time of day would be the best way to tell if it is a shadow or not. I am in the process of looking at the 3D panorama and black and white views from previous days to see if I can determine anything that way.