Pleochroism

I love to observe optical properties in gems and minerals and one of my favorites is Pleochroism.
Pleochroism is the ability of a stone to display two or more colors when viewed from different angles. Some good examples are Kunzite, Tanzanite and Cordierite
Good cutters know exactly how to orientate the stone to be viewed from the best angle. Like for example a light pink Kunzite shows a much stronger pink color when viewed from the c-axis. So the best way to cut it, is to put the table of the stone where the c-axis is. Dichroism is basically the same thing, although a dichroic stone only shows two colors while a Pleochroic can show more than two. I came across a small lot of Cordierites that show perfectly the pleochroism on Cordierites (Iolites):