Stone Structure in Mars Taken by NASA Rover

According to the image timestamp, (2006). The image is from Sol 728.

It's so hard to judge the scale of the thing. How far away is it from the rover? Does anyone know the approximate dimensions?

Clearly, aliens......

But for real, what it is?

looks to me like a larger version of that porous looking big rock on the left

I'd say thats exactly the answer you're looking for.