According to the info snippet describing Arcanists in the webby (as quoted by K'dath), the Arcanists need to inscribe gemstones to be able to summon Carbuncle. I'd assume that both summoners and scholars require a similar technique to do the same with their own creatures. I do not think they consume it, though. They are more likely used as catalysts for the wizard's own aetheric gauge (what mechanically we know as 'mana').
If I had to speculate as to what Carbuncles are, I'd say they are probably some kind of aetherical manifestation of mathematics/geometry. Based on the Scholar's questline, where the fairy is shown to have a personality of her own (kinda), I'd argue that this could very well be the case with Carbuncles. The egis probably do, too, based on whatever Primal they are based on. For example, titan-egi, in a cutscene, appears and blocks a magical attack with his face without you actually ordering him so. This implies that, just like Titan, the egi is kind of protective of those he recognizes as 'part of his team', so to speak.
As to what the Elementals with a capital E are, they are basically spirits that excersise power upon the Black Shroud. Unlike the sprites, they can communicate in some way to certain conjurers (called Hearers), who basically act as priests (or maybe envoys) of their will. You can see a Hearer in the Aetheryte plaza, with a bunch of people sitting around, listening to him.
Elementals also have a crapton more of implied power than any sprite. What the Elemental really are is never touched. Think of them as a very strict Mother Nature.
Finally, the big glowing crystals you see dotting many of the landscapes are crystallized aether. The places that were hit the hardest by Bahamut's megaflare (or whatever that thing he did was called) present those formations.
Though some of them could have a different story but, as far as I could tell, they were all caused by the Calamity.
If I had to speculate as to what Carbuncles are, I'd say they are probably some kind of aetherical manifestation of mathematics/geometry. Based on the Scholar's questline, where the fairy is shown to have a personality of her own (kinda), I'd argue that this could very well be the case with Carbuncles. The egis probably do, too, based on whatever Primal they are based on. For example, titan-egi, in a cutscene, appears and blocks a magical attack with his face without you actually ordering him so. This implies that, just like Titan, the egi is kind of protective of those he recognizes as 'part of his team', so to speak.
As to what the Elementals with a capital E are, they are basically spirits that excersise power upon the Black Shroud. Unlike the sprites, they can communicate in some way to certain conjurers (called Hearers), who basically act as priests (or maybe envoys) of their will. You can see a Hearer in the Aetheryte plaza, with a bunch of people sitting around, listening to him.
Elementals also have a crapton more of implied power than any sprite. What the Elemental really are is never touched. Think of them as a very strict Mother Nature.
Finally, the big glowing crystals you see dotting many of the landscapes are crystallized aether. The places that were hit the hardest by Bahamut's megaflare (or whatever that thing he did was called) present those formations.
Though some of them could have a different story but, as far as I could tell, they were all caused by the Calamity.