Astral Resonator

This tool, if right- clicked in the Protector's Enclave will allow you to see Astral Rifts. If you look on your map once you have equipped the resonator, you will find a blue-ish circle that says "astral rift" in it. Go there and there will be an astral rift. Right click the rift to use the resonator on it.

They can be acquired by trading a and be used to extract Astral Diamonds.