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Ok that's interesting... so for chromium oxide used for pigmenting in paints or for cosmetics, we really have no idea what size those "clusters" are?

They may very well be not 0.5 microns?

I would assume that .5 microns refers to the size of a single molecule of CR2O3 (two chromium atoms and three oxygen atoms).. which I intuitively agree with hi_bud_gl that it would always remain...