It's hard to get a read on the size of the spheres in the Mars image but I'm guessing they're something on the order of virtually microscopic up to around a half-inch in diameter. That would fit with what I've observed. Some outcrops seem to consist only of "tinies." But I've also seen "thunderegg" formations larger than full-sized automobiles. It just depends on the conditions of formation. There's another factor I've been wondering about: the effect of Mars' 38% of Earth gravity on geological formations like this.