Raman spectroscopy of hydroxy nickel carbonate minerals nullaginite and zaratite

Raman spectroscopy combined with infrared spectroscopy has been used to study the minerals, nullaginite and zaratite. Raman bands are observed at 3650, 3556 and 3309 cm(-1) for nullaginite and 3609, 3516 and 3336 cm(-1) for zaratite. By using a Libowitzky-type empirical function, estimation of the hydrogen-bond distances of the OH and water units has been made, which vary from 0.268 to 0.332 nm. Hydrogen-bond distances of OH units are less than those for the water units. The observation of multiple asymmetric stretching and bending modes for nullaginite suggests that the carbonate is strongly distorted in contrast to zaratite for which only single bands are found. Raman bands at around 935 and 980 cm(-1) are assigned to OH deformation modes. Copyright (c) 2008 John Wiley & Sons, Ltd.