Also....Spoiler:Is it mandatory that you collect the Earthen Historia/iris gems before talking to Mayvin in Lohgrin? I did collect a bunch of them, partly at my sister's request (at least all the ones the party seems to want you to get by that point about General Heldalf), but can you actually proceed in the main story without getting all of those or not?
Spoiler:
It is, unfortunately. I wish they had made you get them before this point, because backtracking for some is really annoying since some require fights that are really weak and pointless by that point in the game. But yes, you have to get them. You can locate them easily, though. Talk to Rose on the conversation starters that have purple stars. I don't think all of them lead to Iris gems, but most of them should. It should be pretty easy to tell which do and don't. Like the one about the crucibles doesn't bring you to any. Haaaave fun!