Tourmaline spectra.

	Thick section of a tourmaline crystal cut perpendicular to the optic axis. This section is thus not pleochroic. The spectrum is shown below. The small absorption peaks in the visible part of the spectrum are produced by Mn³⁺ absorptions. These transitions give the pink color to the mineral. The intense absorption in the NIR at around 1300 nm, giving no contribution to the color, is probably due to Fe²⁺.

	Highly pleochroic section of green tourmaline. Spectrum is mainly made up of 3 peaks: 700 and 1100 nm being due to crystal field transitions within Fe²⁺ ions and 420-460 nm to charge transfer band. Fe²⁺ in tourmaline structure can replace either Al³⁺ or Mg²⁺. The symmetry of these sites being different, they give rise to transitions at different frequencies. The triplet peak around 1420 nm is produced by the vibration overtones in hydroxyl radicals.