RAMAN-SPECTROSCOPIC IDENTIFICATION OF FIBROUS NATURAL ZEOLITES

Laser Raman microprobe spectra of the natrolite group of zeolites (fib rous hydrous network aluminosilicates) can be used to unambiguously di stinguish among the six members of this group, which is difficult by v isual, microscopic, and X-ray diffraction methods. The natrolite group of zeolites includes the following minerals: natrolite (Na2Al2Si3O10. 2H(2)O), scolecite (CaAl2Si3O10. 3H(2)O), mesolite (Na2Ca2Al6Si9O30. H2O), thomsonite (NaCa2Al5Si5O20. 6H(2)O), gonnardite (Na2CaAl4Si6O20. 7H(2)O), and edingtonite (BaAl2Si3O10. 4H(2)O). Accurate locations of peak maxima are given, and complete Raman spectra (from 100 to 4000 D elta cm(-1)) are shown for each mineral. The individual members of thi s structurally very similar group of minerals can be identified on the basis of the exact Raman peak positions of the two strongest bands ne ar 440 and 535 Delta cm(-1), the number and positions of weaker bands, and the difference in the dependence of peak intensities upon beam po larization direction. Howe, er. the minerals can be especially easily identified on the basis of their strikingly different Raman spectral p atterns in the O-H stretching region (3000-3700 Delta cm(-1)). The num ber and width of peaks in this spectral region correlate with the thre e different types of framework structures that occur among the natroli te group minerals.