The Dependence of the Oxygen Isotope Fractionation in the Hydration Water of CuSO₄ · 5 H₂O on the Crystallization Temperature

Abstract

The fractionation of the oxygen isotopes in the water collected by stepwise dehydration of CUS04-5H20 has been measured for the crystallization temperatures 25, 40 and 50 °C. From X-ray and neutron diffraction studies it is known that three different kinds of water, differing in their binding in the crystal, exist in CuS04 , 5 H20. On the basis of the results reported here it is concluded that isotopic equilibrium exists between the different kinds of water in the crystal and the mother liquor during the crystallization process. In addition it is shown that on stepwise dehydration the water molecules from the different types of sites can be separated. Consequently, the measurements provide the possibility to determine crystallization temperatures from intracrystalline oxygen isotope fractionation alone. Possible applications in isotope geothermometry are discussed.