Grandidierite
Grandidierite is a rare mineral that was first discovered in 1902 in southern Madagascar. The mineral was named in honor of French explorer Alfred Grandidier who studied the natural history of Madagascar.
Grandidierites appear bluer in color the more iron they contain. A recently discovered gemstone, blue ominelite is the Fe-analogue to grandidierite.
Grandidierites display strong trichroic pleochroism. That means they can show three different colors depending on the viewing angle: dark blue-green, colorless, or dark green.
While trichroism can usually help distinguish grandidierites from other gems, lazulites can occur with blue-green colors and show colorless/blue/dark blue pleochroism. Nevertheless, lazulites have somewhat higher refractive indices and specific gravity. Grandidierites also have greater hardness.
