Abstract

Laser Raman microprobe spectra of the natrolite group of zeolites (fibrous hydrous network aluminosilicates) can be used to unambiguously distinguish among the six members of this group, which is difficult by visual, microscopic, and X-ray diffraction methods. The natrolite group of zeolites includes the following minerals: natrolite (Na2Al2Si3O10.2H2O), scolecite (CaAl2Si3O10.3H2O), mesolite (Na2Ca2Al6Si9O3.8H2O), thomsonite (NaCa2Al5Si5O20.6H2O), gon2 nardite (Na2CaAl4Si6O20.7H2O), and edingtonite (BaAl2Si3O10.4H2O). Accurate locations of peak maxima are given, and complete Raman spectra (from 100 to 4000 Delta cm-1) are shown for each mineral. The individual members of this structurally very similar group of minerals can be identified on the basis of the exact Raman peak positions of the two strongest bands near 440 and 535 Delta cm-1, the number and positions of weaker bands, and the difference in the dependence of peak intensities upon beam polarization direction. However, the minerals can be especially easily identified on the basis of their strikingly different Raman spectral patterns in the O-H stretching region (3000-3700 Delta cm-1). The number and width of peaks in this spectral region correlate with the three different types of framework structures that occur among the natrolite group minerals.

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