Thank you for the comments on the photography. I've been at it for a very long time.
Yes, it seems we are dealing with a subject that has been very easy to overlook; the purity of RiO.
I have you and Min to thank for this revelation.
I had a similar experience with RiO going birds-egg speckled. See attached
Interesting to note that the normally white tin was colored dark ivory overall in addition to the dark crystal clusters.
The iron and tin were used in a high-calcium mat formula.
I'm not sure if the result is from the quality of iron or the combination of iron and calcium.
Ball milling will take care of the speckles. Min