The color and spectroscopic properties of iron-bearing tourmalines (elbaite, dravite, uvite, schorl) do not vary smoothly with iron concentration. Such behavior has often been ascribed to intervalence charge transfer between Fe2+ and Fe3+ which produces a new, intense absorption band in the visible portion of the spectrum. In the case of tourmaline, an entirely different manifestation of the interaction between Fe2+ and Fe3+ occurs in which the Fe2+ bands are intensified without an intense, new absorption band. At low iron concentrations, the intensity of light absorption from Fe2+ is about the same foe E\\c and E perpendicular c polarizations, but at high iron concentrations, the intensity of the E perpendicular c polarization increases more that ten times a much as E\\c. This difference is related to intensification of Fe2+ absorption by adjacent Fe3+. Extrapolations indicate that pairs of Fe2+-Fe3+ have Fe2+ absorption intensity ~200 times a great as isolated Fe2+. Enhanced Fe2+ absorption bands are recognized in tourmaline by their intensity increase at 78 K of up to 50%. Enhancement of Fe2+ absorption intensity provides a severe limitation on the accuracy of determinations of Fe2+ concentration and site occupancy by optical spectroscopic methods. Details of the assignment of tourmaline spectra in the optical region are reconsidered.