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.
On the surface, the githyanki and the krivian ghouls have some of the best skilled crystal weavers. These craftsmen create crystalline objects for storing energy. They create things as small as jewelry to psionically grown core tanks on the Eye of Gith. These containers are used to hold either positive or negative energy. The sources for filling these containers are energy rifts.