Waterstar

Waterstar, also called achroite or colorless tourmaline, was a rare fancy stone.

Description
Waterstar was a colorless and transparent gemstone. Gem-quality stones had to be flawless and could yield large faceted jewels that sparkled. A typical specimen had a base value of 100 gp.

Powers
Waterstar, like all tourmalines, could absorb any spell cast upon it and immediately convert it into three lightning bolts that blasted outward from the crystal facets. This act consumed the gem in the process.