Probably been staring too long :)
Check out this picture taken that same Sol on that same rock.
A very nice blueberry, and what is that donut object to the lower left?
If this rock was on Earth, I would say it is limestone. While it is not limestone, I bet it formed in a similar fashion.
And I am still perplexed by the spheres. I think the verdict is still out about their origin.
