Board Thread:News and Announcements/@comment-21547349-20150826152644/@comment-7326455-20150926062549

When you reach a sufficient level, you'll get access to the Jeweler, which lets you combine crystals into shinier ones. Requires too many crystals, in my opinion, though. I don't recall what level it was - eight, probably. Maybe seven. The blue ones come from Cold. You don't have to place anything there, they just spawn around the edges, same as the green ones.

It's basically the same as for any tablet game - if you can't seem to do something, level up and try again.