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Substitution of Ca, Mg and Sr in siderite and its impact on cell edge lengths

Sedimentary siderites commonly show minor amounts of structural Ca, Mg, Mn and Sr. All elements (except Mn2+) have ionic radii different from Fe2+ and change, therefore, the cell edge lengths of siderite. Since the cell dimensions of the siderites can be measured with high precision by X-ray diffraction, a connection of these values with the chemical compositions of the fluids, from which they have grown, would allow to reconstruct the pore fluid chemistry during the diagenetic growth of sedimentary siderites.

The system Fe-Ca-CO3 has been investigated decades ago with synthetic samples by relating the chemical composition of the fluid to the chemistry of the siderites, but up-to-date, no data are available for cell edge lengths. The aim of this work is to desing a crystal growth experiment in a mixed-flow reactor, where steady-state conditions of siderite growth can be related to the chemical composition of the growing fluid. The siderites will be characterized with X-ray diffraction (Rietveld analysis) and by wet-chemical analyses. Relationships between the amounts of substituting cations and cell edge lengths will then enable to reconstruct the fluid chemistry of siderites formed in the Tertiary sediments of Hambach.

Start of work: Immediately
Supervision: Pieter Bertier, Helge Stanjek
Level: BSc or MSc, AGW preferred