The photo shows the outcrop called Kirkwood which is chock full of a dense accumulation of objects that look like small spheres.
Steve Squyres from N.Y. Cornell University stated that “This is one of the most extraordinary pictures from the whole mission,” Although Kirkwood presents a geological mystery NASA is not strange to similar looking formations. Opportunity first seen iron-rich spherical formations back in 2004. These were called blueberries.
Squyres thought that the strange formations found by the rover now look similar at first glance with the Martian blueberries:
“We immediately thought of the blueberries, but this is something different. We never have seen such a dense accumulation of spherules in a rock outcrop on Mars.”
Although these strange formations are currently analyzed they will still remain a geological mystery until scientists can explain how these were formed.