Iol

Iol, also known as violet stone, was the name by which iolite (cordierite) was commonly known in the Realms. Such stones were sacred to Deneir, the Scribe of Oghma.

Description
This semi-precious stone was predominately blue in hue, but its color changed with viewing angle, from dark blue to straw-yellow. Small iols could be transparent but larger stones tended to have inclusions that could cause a star-like effect or, in the case of trapped hematite crystals, a flash of golden color much like sunstones. Iols were usually facet-cut to best display the stone's color change. A typical iol had a base value of 50 gp.

Powers
Iol stones were the best component for use in making ioun stones.

Rumors and legends
Faerûnian legends said this gemstone had a strong affinity for magic, but few knew of its connection to ioun stones.