I have been studying Geology for a couple of decades now, and I am at a loss for an explanation. Leave to Mars to come up with something new- I mean that in a good way.

The one explanation that I keep pushing away, but it keeps creeping up the back of my mind, is that (let me make sure no one is looking and whisper it to you) is that they have a biological origin. The skeptic in me says that there has to be a Geological explanation, but the things are evenly distributed in the parent rock, they are of a different composition from the parent rock, they are spherical and roughly all the same size, and they are found in a fossilized shoreline environment.