I haven't really paid that much attention honestly. I've been making a killing DE'ing rings and necks for enchanting mats to be bothered with blue gems which have already tanked in price on my realm. Good thing there is a huge abundance of ore out in the world, I can't even quest without tripping over a node.
I've just been doing the daily discovery with blues and thats about it. I'll pocket the rest until I can start using them for gear.
Well if ghost iron is supposed to be the first tier of ore, and trillium the second (I think), then ghost iron would have a lower chance of rare gems. It was the same thing with BC fel iron got less blues than adamantite, etc.
I make ornate bands and shadowfire necklaces. I DE the green ones and AH the blues as is since those sell for more then the DE'd product. I then take the spirit dust and turn those into mysterious essences and sell those. I don't really sell the spirit dusts since 5 of those sell for less then a mysterious essence and it takes 5 spirit dust to make 1 essence so you end up making a few extra gold. I don't turn the mysterious essences into blue gems since those sell for less then the 5 mysterious essences it takes to make it. At least on my realm the mysterious essences is the way to go for now.