Evolution of fumarolic anhydrous copper sulfate minerals during successive hydration/dehydrationстатья
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Дата последнего поиска статьи во внешних источниках: 4 июня 2021 г.
Аннотация:Hydration processes of primary anhydrous minerals as well as dehydration of the hydrated phases are relevant not only for answering geochemical and petrological questions, but are also interesting in the context of the theory of «Evolution of minerals». Our study of the evolution of anhydrous exhalative sulfates in hydration and dehydration processes has demonstrated the complexity of the processes for a number of minerals from the active high-temperature fumaroles of Tolbachik volcano (chalcocyanite CuSO4, dolerophanite Cu2O(SO4), alumoklyuchevskite K3Cu3AlO2(SO4)4, and itelmenite Na2CuMg2(SO4)4). The hydration and dehydration experiments with all four studied minerals were carried out using PXRD. A typical structural characteristic of several anhydrous copper sulfate minerals of fumarolic origin is the presence of oxygen-centered OCu4 tetrahedra. These are absent in the structures of all known hydrated minerals or synthetic compounds of the class under consideration. Hydration of minerals initially containing O2- anions as parts of oxocomplexes, proceeds with sequential formation of a large series of hydroxysalts. On the contrary, hydration of itelmenite with a relatively complex “initial” structure without additional oxygen atoms, which are strong Lewis bases, results in formation of simpler hydrates. The lower the temperature and the larger excess of water, the higher hydration numbers are observed for cations. Ultimately, the water molecules expel the bridging sulfate anions from the metal coordination sphere yielding relatively simple fully hydrated structures.In addition, in the general context of the theory of the evolution of minerals, it is obvious that anhydrous fumarolic high-temperature minerals form a separate family.