BÖTTCHER, M.E. & GEHLKEN, P.-L. (2004):
Stable isotopes, elemental, and structural changes upon dehydration of gaylussite.

– Ber. Dt. Mineral. Ges., Beih. z. Eur. J. Mineral 16/1: 19.
The hydrated disodium-calcium dicarbonate mineral gaylussite (Na2Ca[CO3]2 · 5H2O) occurs in oil shales and in sediments of evaporated lacustrine lakes as the Green River formation (MILTON & FAHEY 1960) and Searles Lake, California (SMITH 1979). The stable isotopes of carbon and oxygen are extremely usefull in deducing carbonate formation conditions and may preserve informations about the paleoenvironment. However, upon diagenesis hydrated minerals may undergo dehydration reactions (BÖTTCHER & GEHLKEN 1996, BÖTTCHER & REUTEL 1996). In the present study the effect of temperature-induced dehydration of natural sedimentary gaylussite on the stable isotopic composition was investigated.
In the present study, stable carbon and oxygen isotope fractionation during experimental dehydration of gaylussite was investigated between 20°C and 800°C. The influence of solid phase dispersion in dissolved water upon heating was considered, too. The elemental composition was followed by elemental analysis and the structural changes by FTIR spectroscopy.
Gaylussite is dehydrated at temperatures between 63°C and 90°C, and anhydrous α-Na2Ca[CO3]2 is formed (BÖTTCHER & GEHLKEN 1996, BÖTTCHER & REUTEL 1996). The newly formed solid was enriched in 12C and 16O compared to the original solid. The stable isotope effect becomes more pronounced at temperatures above 200°C. In general, 13C contents in the solid decrease with increasing temperature. C and O isotope shifts decrease under isothermal conditions with increasing water contents. For oxygen isotopes this is due isotope exchange with an evaporating solution. Between 500°C and 800°C the carbonate solid is decarbonatized and stable isotope fractionation is controlled by interactions between metal oxides and the atmospheric gas phase.