Soooo...this week's emissary chest requires Blue Prophet Crystals. Perfect, I've hoarded a lot of crystals last week to exchange them for these!
...and so I did that!
I've traded 20 Blue Shards for 1 Blue Prophet Crystal
Then I've traded around 6 Green Prophet Crystals for Blue Prophet Crystals, all of that at Asura Karma Vendor in Eye of the North.
BOOM, all my shards gone, all my crystals gone, with just 1 Blue Prophet Crystal in my currency/wallet.
I'm...desperate right now.