Crystallography and mineralogy of nickel carbonate hydrate

The preparation and X-ray powder diffraction pattern of nickel carbonate hexahydrate, NiC03-6H20(cr), were first described by Rossetti-Fran9ois [52ROS]. The crystal system is monoclinic-prismatic, space group C2/c, cell dimensions qq = 10.770 A, bo = 7.299 A, Co = 18.681 K,Z=% 94.00°, = 1464.94 A, yo(obs.) = 1.97 g-cm , yo(calc.) = 

975 g em (according to JCPDS-ICDD cards 12-276 and 24-523, where the empirical formulae are NiC03 6H20(cr) in the former and NiC03-5.5H20(cr) in the latter). 

The natural occurrence of hellyerite, NiC03-5.5H20(cr), in the Lord Brassey nickel mine near Heazlewood (Tasmania), was first reported by Williams et al. [59WIL/THR]. The Mohs hardness is 2.5, its luster is vitreous (glassy) and its streak is white. The X-ray powder diffraction pattern was found to be similar to that of synthetic nickel carbonate hexahydrate, prepared by the method of Rossetti-Fran9ois. 

The single crystal structure determination by Threadgold [63THR] of the natural product may be not perfect due to extensive twinning of the material. Hellyerite forms predominantly twin crystals to enhance the low crystal symmetry. Therefore the crystal structure needs to be refined to resolve its subtleties. 

With Equation (V.105) the following value can tentatively be used for the heat capacity of NiC03 5.5H20(cr)  

---