User blog comment:Maki Kuronami/Lesson 14: No Rapier Wasps. At least we get a Mega Ursa./@comment-168.156.98.136-20131025174428

I thought the line between Aura and Dust was simple.

Aura is internal; if Weiss was attacked while her rapier was in the shop, she would still have her glyphs.

Dust is external; somebody whose aura was not unlocked could still be wandering around with a shotgun and Dust shells.

I suspect that Semblance is the first level of Aura display without a weapon - it's what comes naturally. So Jaune's Semblance appears to be a mix of invulnerability and rapid healing.