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The strong pleochroic band of brown tourmaline at around 24000 cm−1 in the E⊥ c photoacoustic spectra was assigned to d-d(6A1→4A1, 4E) transition of Fe and to charge transfer of Ti, that in the E//c spectra being entirely assigned to charge transfer of Ti. The analysis of the photoacoustic signal intensity vs. chopping frequency gave the thermal diffusivity constant of tourmaline as α=0.15 cm2/s.
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Sugitani et al. (1981) studied this question.
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