Sample 643 looked somewhat "blotchy" in macroscopic appearance, with some sections slightly more translucent and other sections slightly more opaque. I think Hendrik told me this sample partially melted? Anyway, I tried to look first at a more translucent section ("A" series) and then a more white/opaque section ("B" series).
643_compositeA1A Series
In the A series, some sections underwent almost no change when viewed in the SEM and seemed to have very low MPH content. There was in fact some MPH in these sections, but I had to scout around a bit. "A" series photos are attached here. There are still a few more photos I haven't yet compiled, but they show nothing different from what's here. (The other photos are the ice-rich sections that simply look somewhat "massive", like photo 1 in the set here.)
643_compositeB1B series
More MPH appears to be in the whiter section, which is the "B" series
643_compositeB2