Thermochimica Acta, Vol.435, No.1, 68-70, 2005
Thermodynamic properties of lithium mica: Lepidolite
Calorimetric measurements were made on natural sample of lepidolite having the composition (K0.80Na0.05Ca0.07Rb0.16Cs0.03)(Li1.34Al1.40Fe0.013+)[Si3.25Al0.75O10]F-1.80(OH)(0.20) from Na-Li-type rare-element-rich pegmatites of East Sayany, Russia. High-temperature enthalpy increments were measured with a Tian-Calvet calorimeter at 444-972 K using the drop method. The resultant C-p.m.(o)(T) equation in the interval T= 298.15-972 K was calculated: C-p.m.(o) = 316.10 + 228.12 x 10(-3) T-50.10 x 10(5) T-2 (JK(-1) mol(-1)) [+/- 0.4%] and the value of C-p.m(o) (298.15 K) = 327.8 J K-1 mol(-1) was obtained. The standard molar enthalpy of formation from the elements was determined by high-temperature drop solution calorimetry in molten lead borate at T= 973 K. The value of Delta(f)H(m)(o) (298.15 K) for lepidolite was found to be -6201 +/- 18 kJ mol(-1). The thermodynamic properties of lepidolite of idealized composition KLi1.5Al1.5[Si3AlO10]F-2 were estimated based on the experimental data obtained. (C) 2005 Elsevier B.V. All rights reserved.