The Ti-influence on the tourmaline color

Journal of the Brazilian Chemical Society

Warde A. Da Fonseca-zang²  Joachim W. Zang²  Wolfgang Hofmeister¹ 

[1] ,Centro Federal de Educação Tecnológica de Goiás Área de Química Goiânia GO ,Brazil

关键词: titanium;    IVCT effect;    tourmaline;   

DOI  :  10.1590/S0103-50532008000600020

来源: SciELO

【 摘 要 】

Titanium was examined in different black tourmalines by spectrophotometric analyses in the region between 12500 and 27000 cm-1 (800-370 nm) using a microscope spectrophotometer MPV-5P, Leitz (Germany), and chemically analyzed on an electron microprobe Camebax Microbeam, Cameca (France) in WDS Mode. Fourteen tourmaline samples with their face oriented parallel to the principal axis, cut and polished down to thin sections, showed polarized spectra of two broad absorption bands at approximately 14000 cm-1 (715 nm) and 24000 cm-1 (417 nm). Precision thickness measurements were used to calculate the absorption coefficients α. For the absorption around 24000 cm-1, a linear correlation was observed between α and the TiO2 content (mass %). Another linear regression was observed between α and the product of TiO2 and FeO (%) contents. Cations located in the Y- and Z-octahedrons of the structure that are connected over edges might contribute to intervalence charge transfer transitions (IVCT) between Ti3+-Ti4+, Fe2+-Ti4+ and Ti3+-Ti4+-Fe3+.

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