Fractionation in magnesium minerals
The upper continental crust is abundant in magnesium in the form of primary silicate minerals and mantle derivatives, and have a narrow fractionation range, with delta between -0.1 and -0.3 per mille. However, low-temperature weathering processes can lead to high fractionation of carbonate and secondary silicate minerals relative to the upper continental crust, spanning a range from -5.2 to 0.92 per mille, with carbonate minerals becoming isotopically light and secondary silicate minerals becoming isotopically heavy. While this is known, uncertainty remains regarding the details, sense and magntiude of isotopic fractionation involving magnesium minerals. We propose to study fractionation processes involving magnesium computationally. In particular, we will focus on the fractionation in brucite and epsomite vs solution phase magnesium hexa aqua. In practice, this is done by generating the hessian for a carefully constructed cluster -- in the case of mineral phases the clusters are made to be neutral using Pauling bond strength conserving terminal partial charges -- and then computing the reduced partition function ratio to obtain fractionation factors. This work is of general importance in geochemistry and exobiology via chlorophyll, in addition to increasing our understanding of isotopic enrichment in general within inorganic complexes.