Quote Originally Posted by Everon
I think Dianna sold the pyrite to Horo. Notice the large feathers?

Whether she's trying to help Lawrence or hinder his efforts to crash the market, though, is anyone's guess.
Though Horo now knows about Dianna's existence through the letter, I doubt she actually knows what Lawrence is planning. Even Amarty, who's been trading for a good while, only recently learned how to buy with credit.

I'm sure it was Amarty who bought the pyrite, and gave the feathers to Horo as a gift. It also shows how he's already buying with credit, and his confidence shows he (thinks he) knows what he's doing, supporting previous remarks that he's a prodigy on the regarding trade.