The official GemStone IV encyclopedia.
Cordierite is a mineral that is commonly of a blue color, although its color shifts depending on the angle it is observed from.
List of Cordierites
a blue cordierite
|Description: The unusual color of a blue cordierite could be compared to a light blue sapphire with a purplish tint. Sometimes called a "water sapphire," cordierite has an entrancing color-changing ability. When seen from one direction, the crystal is a clear blue-violet. But as it is rotated, the color changes first to yellowish-grey, then back towards light blue.|