You order your courtiers and messengers to start looking for a Wizard.
984 AD, Midwinter
The caravan from Damdamia arrives to exchange gemstones for leafworm cloth.
5to6
You get absurdly high profits from re-selling it to your nobles! Coffers upon coffers of coinage arrive in the Treasury! The arrival of gold nuggets from your mines and another load of gemstones only secures your future wealth.
The Damdamian merchants aware of your 'plague' going, and say they won't arrive next year if it won't be safe to travel. Curses.
1
Unfortunately, nobody saw a Wizard anywhere near your Duchy.
The Spymaster walks up to you when you're moping a bit in the gardens one evening.
"My liege, my agents have found the source of the plague."
"Oh?"
"It is the new crystals we mine. After a simple investigation, we determined that first victims where the miners handling the crystals, then their overseers and merchants, and then their clients." You quickly call your guards to inform your dearest wife and your twin daughters from first marriage; all three have bought crystal jewelry few days ago!
"And how did your agents not catch this disease?" The Spymaster hums.
"I have no explanation beyond the fact that the agents who handled the crystals felt their elven moonthread cloaks tingle and fuzz and puff up near these strange crystals. Mayhaps elven magick also protects from the effects of the crystals." You send for another guard; messengers are hastily appropriated to inform everyone in the Duchy to stash the crystal jewelry away from people and for the mines to close operations immediately.
"Any orders, sire?"
A) "No, keep looking for the Wizard."
B) "Yes; cut up all of the moonthread cloaks and send a piece to everyone affected. And maybe to those who handled the stuff, too."
C) "Yes; send for dwarves of Zonalath or somewhere, and ask them to come fix this if they can. Surely if the elven magic interacts with the crystals, they must be somehow to connected to the dwarves."