My Lands: Black Gem Hunting

I have come across a few missions lately where it seems I need black gems, if I don't have any I can buy them to complete the mission. Sorry but you have no chance of me buying any, not a hope in hell. I'll buy PS3 games and even Xbox games for my son, but will never spend a penny here. Let's admit it, why spend money to watch a static screen, you must be mad to do it.

there is the auctions that sell black gems but you need to have atleast 100k just to buy 10
there are ruins that have gems, the larger the ruin number the more gems they have