Vibrational spectra of MIMIII S2 type synthetic minerals (MI = Tl or Ag and MIII = As or Sb)

The far infrared and Raman spectra of four (MMS2)-M-I-S-III type synthetic minerals (lorandite, TIAsS2; smithite, AgAsS2; weissbergite, TlSbS2, and miargyrite, AgSbS2) were studied at room temperature. Their vibrational spectra were compared with the corresponding far infrared and Raman spectra Of (M2S3)-S-III type minerals: orpiment, As2S3 and stibnite, Sb2S3. In spite of different crystal structure of these minerals, a similarity between the vibrational spectra of the three arsenic containing minerals (orpiment, As2S3; lorandite, TlAsS2 and smithite, AgAsS2), on the one hand, and the three antimony containing minerals (stibnite, Sb2S3; weissbergite, TlSbS2 and miargyrite, AgSbS2), on the other hand, has been detected. The observed spectral behavior was discussed in terms of structural similarities and differences between the minerals containing As atoms and the ones containing Sb atoms. Thus, the arsenic containing minerals are characterized by the layer-like structure and the presence of rather similar As-S bond distances (208-236 pm), whereas the antimony containing minerals have sheet-like structure and the variety of Sb-S bond distances, spreading in a wider range of values (241-296 pm). (C) 2003 Elsevier Science B.V. All rights reserved.