George R. Rossman
Division
of Geological and Planetary Sciences, California Institute of
Technology,
Most
tourmalines we encounter are colored by iron, titanium and manganese. Both iron
and manganese are present in the 2+ and 3+ oxidation states. But rubellite
color is dominated by manganese in the 3+ oxidation state. Tourmaline is a
subtle mixture of colors caused by individual ions and by colors caused by
interactions between ions, in particular, between Fe2+ and Ti4+.
Rubellite is both a product of chemistry, namely manganese, and natural
irradiation which oxidizes the manganese from the weakly colored 2+ oxidation
state to the deep red 3+ state.