Some closeup shots on my Z16--I am not sure if the oblique lighting is introducing issues or if something's off with the lens system, it's all a bit ad hoc. But you can still see some better details in there:
I was sure it was mold when I first saw it without magnification. My dad thought maybe electrostatic discharge when he saw the picture. But there is also some on the very top glass surface, and it wiped off when I tried to clean some dust off to get a better picture, so ESD is out anyway. I am starting to lean towards crystallization, though of what I am not sure, nor how it would have gotten there.
Unfortunately the bulk of the camera makes it hard to put this on my Nikon compound, for whatever good that would do.