Raman microscopic study of holmquistite, a Li-bearing orthorhombic amphibole

摘要

The Raman spectra of three samples of holmquistite, a lithium-containing orthorhombic amphibole, from Bessemer City (NC, USA), Barraute (Quebec, Canada) and Brandgraben (Austria), have been measured by Raman microscopy. The OH-stretching region is characterised by bands around 3660, 3645, 3635 and 3615 cm~(-1) assigned to (3Mg)-OH, (2Mg + Fe~(2+))-OH, (Mg + 2Fe~(2+))-OH and (3Fe~(2+))-OH, respectively. Based on the ratio between the 3645 and 3660 cm~(-1) bands Fe~(2+)/(Fe~(2+) + Mg~(2+)) ratios in the M_1 and M_3 sites were determined to be in the range between 0.35 and 0.45. The 950-1130 cm~(-1) region represents the antisymmetric Si-O-Si and O-Si-O stretching vibrations. For holmquistite from Bessemer City, U.S.A, strong bands are observed around 1022 and 1085 cm~(-1) with a shoulder at 1127cm~(-1) and minor bands at 1045 and 1102 cm~(-1). In the spectra of the other samples these two bands we very weak and accompanied by bands wound 965, 998 and 1061 cm~(-1). In the region between 650 and 800 em4 bands we observed at 679, 753 and 791 cm~(-1) with a minor band around 694 cm~(-1) attributed to the symmetrical Si-O-Si and Si-O vibrations. The region below 625 cm~(-1) is characterised by vibrations related to the deformation modes of the silicate chain and vibrations involving Mg, Fe, Al and Li in the various M sites. The 502 cm~(-1) band is a Li-O deformation mode while the bands at 456, 551 and 565 cm~(-1) we Al-O deformation modes. OH-libration and translation modes we observed wound 300, 530, 582 and 613 cm~(-1).