On the nature of Carbuncle

[Anonymoose]

Why would the gem for Ramuh be Iolite <...> what about Garnet for Ifrit, :P.

Linked to the ilvl 90 gems maybe <...> Topaz, Iolite, Sapphire, Diamond, Emerald and Ruby

Bingo. If Topaz and Emerald are on the same tier, in the right colors, those would be the rest would be ...

Following the convention pattern