The spheres cut by the RAT have just shown scratches. The naturally split and eroded spheres have been imaged a good many times now, with clear views of the interior. What this has shown me (my view)
1. No glass. No conchoidal fracture. No fracture.
2. Granular. No radial structure. Little or no evidence for a skin, or concentric structure.
3. Only internal structures seen so far:
A) Small spots or holes, sometimes grouped, but lacking symmetry, that erode differentially, resembling seeds in a tomato sometimes.
B) Small black arcs and rings or maybe spheres, possibly volcanic ash shards or microfossil cell walls?
4. No layering whatsoever, even though these are gently wind eroded spheres, and many can be seen in rocks where the layering is much smaller in scale than the spheres, if fact, this is the most typical case, in my opinion. I find Nasa's claim of layering in these spheres to be flatly preposterous! I dont buy the concretion explanation one bit.

One of my candidate theories about the size distribution is that the spheres formed as precipitates at the waters surface within a framework of floating "algal strands," or an algal mat. They could have formed non-biologically, just as well. I think there is a better case for the strands being biological than the spheres. The spheres could grow nice and round and separated from each other by the algal mat due to the wave action. Once they weighed the mat down too much, it would sink, thus limiting the sphere size. Small spheres are seen, but there are very, very few large ones. This theory explains the sphere-stem linkage as a casual but coformulative one.

My other theory is that the stem is indeed attached to the sphere as an organism that grew up from the bottom sediments, possibly with other soft parts that we may not see, or that we are seeing, but that these detached easily and are preserved as these abundant "voids" in the rock. Tha Nasa explanation of these voids as dissolved salt crystals - well, most of these voids are curved and irregular, they dont look like ex crystals to me. If they would just micro image some of these better preserved and delicately eroded spheres with stick like stems, we might get a better understanding.