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    STUDIA GEOLOGIA - Issue no. 3 / 2003  
         
  Article:   ISOMORPHIC SUBSTITUTIONS IN HIGH AND LOW VESUVIANITE STRUCTURE.

Authors:  ELENA YU. BOROVIKOVA.
 
       
         
  Abstract:  Vesuvianite is an ortho-disilicate with complicated chemistry. Its general formula can be written as X19Y13Z18O68T0-5W10, where X is Ca and other large cations occupying 8-coordinate sites, Y are cations occupying 6 and 5-coordinate sites, as Al, Mg, Fe, Ti etc., Z are Si occupying 4-coordinate sites, T is B in 3 and 4-coordinate sites, and W are monovalent and divalent anions: OH-, F or O. Depending on atoms ordering in the structure, vesuvianite crystallizes in P4/nnc (high) or P4/n (low) space group. Low vesuvianite occurs in metamorphic rocks formed at low temperatures [< 300ºC, compared to those containing high vesuvianite (400 - 800ºC)]. A collection of more than 50 vesuvianite samples was investigated by a number of analytical methods such as electron microprobe analysis, IR-spectroscopy, Mössbauer spectroscopy and others. Vesuvianite samples were separated accordingly to their space groups, identified by IR-spectra. ...  
         
     
         
         
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