Aether Ash

A material left behind by spells when they're cast. Under normal circumstances, the amount is small enough that it goes unnoticed, but when many spells and powerful ones at that are thrown about in an area it starts to coat the ground and surfaces.

It's not a true ash, more like a fine multicolor sand. It's fairly innert, unless particular processes are used upon it, which can then be refined down into condensed Aether once more. Not necessary for the average mage, but factories that rely on crystals and other pre-packaged Aether sources will often collect the ash to do just that.