POE Prime Chaotic Resonator is a socketable currency. It is required to craft a rare item by adding specific mods on it. In order to be activated, the resonator should be socketed with fossils. It needs 4 sockets fossils to provide mod effects on items. The currency quite rarely drops in Path of Exile game, but you can buy Prime Chaotic Resonator from other players. The price for it is 38 Chaos Orbs on average, however, it may vary depending on the league.