THE INFRARED SPECTROSCOPY OF VESUVIANITE IN THE OH REGION
LEE A. GROAT
Department of Geological Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z4
FRANK C. HAWTHORNE
Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2
GEORGE R. ROSSMAN
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.
T. SCOTT ERCIT
Canadian Museum of Nature, Mineral Sciences Section, Ottawa, Ontario K1P 6P4
Abstract
Many important substitutions in vesuvianite involve variable H, and those that do not still perturb the
local environment of the OH- anions. Consequently, infrared spectroscopy of the OH fundamental
and overtone regions is an important probe of local order. We have examined a series of vesuvianite crystals
carefully characterized (by electron-microprobe analysis, wet-chemical analysis and crystal-structure refinement)
by polarized single-crystal infrared spectroscopy. The crystals span the complete range of chemical
variation reported in vesuvianite, and the spectra show tremendous variability. There are 13 recognizable bands
(A-M) that can be divided into three types: (1) eight bands due to absorptions at the OH site;
these result from different local cation and anion configurations at nearest-neighbor and next-nearest-neighbor sites; (2)
four bands due to absorption at O(10); these result from different local cation and anion configurations at
nearest-neighbor and next-nearest-neighbor sites, and (3) a low-energy electronic absorption band. Boron
is incorporated into the vesuvianite structure primarily via the substitution B + Mg 2H + Al.
In boron-rich vesuvianite, the four bands J-M are not present, indicating that H has been completely replaced by
B in the vicinity of the O(10) site. Although lacking the fine detail of the principal-stretching region, the overtone spectra
are equally characteristic of this B H substitution. The spectra in the principal OH-stretching region extend over a
very wide spectral range (3700-3000 cm-1), and show two features that are of general importance in the
quantitative interpretation of such spectra: (1) the band width increases significantly with decreasing band-frequency
(from 20 cm-1 at 3670 cm-1 to 120 cm-1 at 3060 cm-1), and (2) the band intensity is (nonlinearly) correlated with band
frequency (in addition to H content). These two features are of significance in quantitatively fitting spectra by numerical
techniques, and in relating band intensities to compositional features.
Keywords: vesuvianite, infrared spectra, electron-microprobe analysis, crystal structure, hydroxyl.