[John H K]

Diatoms are VERY small. Many orders of magnitude smaller than these.

[doodad]

Hey good morning. Isn't this incredible? I am leaning very hard now on water and a concretionary source for this to occur. I can't think of any metamorphic state that would yield spheres unless it was a weird type of retrograde metamorphism affecting certain phenocrysts.

[blam]

"Diatoms are VERY small. Many orders of magnitude smaller than these."

Okay, thanks. (Next headline: Giant Diatom Fossils Found On Mars, lol)