Theurgy Jewel (Refined Gemstone)

 is an Alchemy craftable item. This cut Jewel gems can be socketed into crafted Rings and Necklaces (also at alchemy table). A socketed Jewel adds attunement to that gem's magical element (and penalized attunement to the opposing element) while the equipment is worn or wielded. This stacks with attunement from passive skills.