Garleans, Magicite,and aetherites

[Danouri]

So I had I thought, Magicite like we find on eureka can block the flow of aether, all purebred garleans are born with that pearl in the "third eye" position. what if that is a small piece of magicite that the garlean body produces that is an evolutionary throw back but now prevents the use of aether

[ObsidianFire]

It's canon that the Garlean 3rd Eye and the inability to manipulate aether are two different things. They just so happen to crop up in the same race. Raw skill at manipulating aether arrives from person to person as it is, it's just that the Garleans as a race can't do it easily. Until Zenos started messing with the Resonance that is...

The 3rd Eye apparently gives Garleans better spacial awareness which is linked to them being very good with understanding how magitek works. It probably also accounts for why they like airships and aerial combat. Interestingly enough, the other race biologically inclined to spacial awareness is the Au Ra (their horns process sound differently for a similar effect) and they also really like aerial combat as well.

As for the inability to manipulate aether... we still don't know why that is. The Ivalice raids have confirmed it is not a new development and has been around as a racial trait for a while though.