Crystal Weaving is a psionic skill that allows one to shape living crystal. This living crystal is scattered across the Underdark and in some areas of such quantity that it serves as living areas. When it runs out, a group of crystal weavers can grow new crystals. This is a tiresome undertaking requiring a lot of time and experience.
The githyanki of Har'kish and the Pyrmidian Ghouls have some of the best skilled crystal weavers. They craft crystalline objects for storing energy, crystal rods, obelisk charges and vortex cells.