I fight to keep arms at my sides, down
from where they have been waving
black signs in orange skies.

Dave: Oh, so you want to get technical on me! Well… silica doesn’t precipitate out of solution in shallow marine enviroments–remembered from Harvey Blatt’s “Petrology”!
I actually have spent more time with a much older text that hadn’t landed on pat answers and allowed that the formation of drusy quartz remain mysterious. You’re probably right about pelagic being wrong!

Teju: Thanks for caring!