Minerals from Macedonia. Part XIX. Vibrational spectroscopy as identificational tool for some sheet silicate minerals

The results of the identification of six sheet silicates originating from the Republic of Macedonia: chrysotile, Mg3Si2O5(OH)4; antigorite, (Mg,Fe2+)3Si2O5(OH)4; talc, Mg3Si4O10(OH)2; clinochlore, (Mg,Fe2+)5Al(Si3Al)O10(OH)8; cymrite, BaAl2Si2O8·H2O and montmorillonite, (Na,Ca)0.33(Al, Mg)2Si4O10(OH)2·nH2O, using vibrational spectroscopy were presented. The above mentioned minerals show IR spectral similarities in the region below 1200 cm−1, mainly due to their common structural characteristics being mostly expressed in the case of isomorphous chrysotile and antigorite. Three medium bands observed in the highest wavenumber region of clinochlore originate from the stretching vibrations of the three crystallographically different OH groups. A sharp peak at 1630 cm−1 was noticed only in the IR spectra of cymrite and montmorillonite being discriminative pattern between hydroxide and water-containing minerals. The similarities between the Raman spectra (1200–100 cm−1) were less expressed confirming that Raman technique is more sensitive to compositional changes as well as to structural disorder. Identification was based on the comparison of the obtained results with the literature data for the corresponding minerals originating from other localities all over the world.