The Aether is an invisible, intangible force that is, nevertheless, known to exist and responsible for the existence of life after the Shattering. Crystals existing within the islands are able to interact with the Aether and become buoyant, keeping the islands themselves airborne. Attempts to mine the crystal are mostly unsuccessful, sometimes even disastrous- as improperly mined crystal can fracture and become useless for channeling Aether in any form (including to float).
If a handheld crystal can be obtained, a rare few individuals have a natural ability to Channel the Aether into certain effects. Primarily these are small enhancments, or utility abilies (such as cleaning, making things stronger/minor repairs, etc), tho it is not unheard of for somewhat more visible things to be done (such as the abilities of the ‘Sky Ninja’).