This paper presents the results of the thermochemical study of hydrous copper sulfate CuSO4 center dot 5H(2)O performed on a high-temperature heat-flux Tian-Calvet microcalorimeter. The samples of two natural chalcanthite (Kosmurun ore deposit, Kazakhstan, and Lavrion deposit, Greece) and synthetic hydrous copper sulfate (blue vitriol) were characterized by X-ray microprobe analysis, X-ray powder diffraction, thermal analysis, FTIR and Raman spectroscopy. The enthalpy of dehydration at T = 298.15 K was measured, and the standard molar enthalpies of formation from the elements were determined by the melt solution calorimetry in accordance with Hess's law. The values of Delta H-f(m)0 (T = 298.15 K) were found to be -(2267.2 +/- 4.1) kJ.mol(-1) for natural chalcanthite and -(2272.6 +/- 6.0) kJ.mol(-1) for synthetic hydrous copper sulfate (blue vitriol). (C) 2016 Published by Elsevier Ltd.