Who said that a Monolith was going to be rectangular?

maybe it's Rama, or a crashed UFO? The conspiracists are going to love this one...

Geologically, it's something unusual. Maybe fresh basaltic lavas - very dark in colour, but there's a 3D geometry that I don't understand. As dtb says, it could just be the central peak, but this is more than a shadow. It's blacker than anything else in shot, by far.

Could be lavas flowing down one flank of the central peak. I'd like to see this under different lighting conditions to make comparisons. I remember some very strange central peaks on Mercury/Mariner photos...