Graphite

"Felum En Dial!"
Graphite is a flat grey, hexagonal crystal
You can expend a Ki point while holding this stone to call forth a bolt of hot lightning from the stone.
All creatures in a 15 ft. line must make Dexterity saving throws, on a failed save, those within the line take (2d6/Ki point) points of lightning damage, and half as much on a successful save.