Aetheric fossil is a stackable currency item. You can buy POE aetheric fossils from Niko the Mad for 1000 azurites, obtain it by farming in Azurite Mine from Sulphur Vents or exchanging with other players for Chaos Orb. This one of fossils can also be obtained by means of vendor recipes. In Path of Exile, it increases the spawn weights of all mods with caster tags by 10 and attack tags by 15. In order to affect item crafting, aetheric fossils should be placed into the resonator.