Raman microscopic study of some borate minerals: Ulexite, kernite, and inderite

Three borate minerals-inderite, kernite, and ulexite-have been studied by Raman microscopy in the region between 4000 and 100 cm(-1). The spectra are very complex due to the presence of foul possible boron clusters in either trigonal or tetrahedral coordination. All three minerals contain clusters containing one or more of both the trigonal and tetrahedral boron clusters. Ulexite is characterized by bands at 3490, 3433, 3401, 1133, 1111, 1005, 745, 668, 639, 617, 602, 551, 491, 475, 421, 412, 367, and 305 cm(-1). Kernite is characterized by hands at 3585, 3543, 3421, 3352, 3247, 3122, 2987, 2855, 2729, 1465, 1388, 1349, 1061, 929, 880, 869, 841, 801, 778, 736, 584, 541, 494, 458, 424, 386, 372, 316, and 301 cm(-1). Inderite shows the most complex spectrum with bands at 3616, 3479, 3365, 3292, 3254, 3127, 3067, 2988, 2931, 2843, 2750, 1397, 1349, 1282, 1249, 1195, 1167, 1138, 1058, 1006, 948, 879, 811, 743, 664, 637, 580, 551, 492, 440, 420, 379, 347, and 313 cm(-1). The region between 3600 and 3000 cm(-1) is characteristic for the ON stretching modes; between 1500 and 1300 cm(-1) one will observe the asymmetric stretching modes of the trigonal boron cluster, whereas the symmetric stretching region is generally between 950 and 850 cm (1). The asymmetric stretching mode for the tetrahedral boron clusters is observed between approximately 1100 and 850 cm(-1), while the symmetric stretching modes are observed between 850 and 700 cm(-1) together with the OH out-of-plane bending modes. The ON in-plane bending modes are visible between 1300 and 1000 cm(-1). Finally, the bending modes for both the trigonal and the tetrahedral boron clusters are found below 700 cm(-1).