Stable calcium isotope fractionation during chemical weathering.

Carbonated hydroxy-apatite (CHAP) was experimentally synthesized in batch-type set-ups by mixing of calcium (Ca)- and phosphate-bearing aqueous solutions and the transformation of calcite powder in aqueous solution between 11&#176; and 65&#176;C (Gussone et al., 2020). Compositional changes of the experimental solution and solid phase products were followed by elemental analysis, Raman spectroscopy, scanning-electron microscopy, and powder XRD. In the mixing experiments, crystallization of CHAP took place following the precipitation of metastable brushite as precursor that was then transformed into CHAP. In the transformation experiments using synthetic calcite as a precursor phase it was found that the reaction at pH values between 7.5 and 7.9 occurs via the direct replacement of calcium carbonate by CHAP.Calcium isotope fractionation led to an enrichment of the light isotope in the solid CHAP compared to the aqueous solution by about -0.5 to -1.1 &#8240;, independent from the experimental approach, and the magnitude was essentially independent of temperature. The metastable brushite formed prior to transformation to CHAP showed a reduced fractionation compared to the CHAP. The observed Ca isotope fractionation into the CHAP lattice resembles that of natural phosphorites and lies within the range of the view existing theoretical and experimental studies.&#160;Reference: Gussone N., B&#246;ttcher M.E., Conrad A.C., Fiebig J., Pelz M., Grathoff G., Schmidt B.C. (2020) Calcium isotope fractionation upon experimental apatite formation. Chem. Geol., 551, 119737The study was supported by German Science Foundation (DFG) to M.E.B and J.F. within the EXCALIBOR project (BO1548/8 and FI 948/7), and to N.G. (GU1035/10), and by Leibniz IOW.

Rate-controlled calcium isotope fractionation in synthetic calcite

Geochimica et Cosmochimica Acta ◽

10.1016/j.gca.2004.05.029 ◽

2004 ◽

Vol 68 (22) ◽

pp. 4665-4678 ◽

Cited By ~ 156

Author(s):

D. Lemarchand ◽

G.J. Wasserburg ◽

D.A. Papanastassiou

Keyword(s):

Isotope Fractionation ◽

Calcium Isotope ◽

Rate Controlled ◽

Synthetic Calcite

Silicon Isotope Geochemistry: Fractionation Linked to Silicon Complexations and Its Geological Applications

Molecules ◽

10.3390/molecules24071415 ◽

2019 ◽

Vol 24 (7) ◽

pp. 1415 ◽

Cited By ~ 1

Author(s):

Wang ◽

Wei ◽

Jiang ◽

Liu ◽

Lei ◽

...

Keyword(s):

Chemical Weathering ◽

Isotope Fractionation ◽

Isotope Geochemistry ◽

Ore Deposits ◽

Silicon Isotope ◽

Core Formation ◽

Silicon Isotopes ◽

Silica Precipitation ◽

Geological Processes ◽

Biological Uptake

The fundamental advances in silicon isotope geochemistry have been systematically demonstrated in this work. Firstly, the continuous modifications in analytical approaches and the silicon isotope variations in major reservoirs and geological processes have been briefly introduced. Secondly, the silicon isotope fractionation linked to silicon complexation/coordination and thermodynamic conditions have been extensively stressed, including silicate minerals with variable structures and chemical compositions, silica precipitation and diagenesis, chemical weathering of crustal surface silicate rocks, biological uptake, global oceanic Si cycle, etc. Finally, the relevant geological implications for meteorites and planetary core formation, ore deposits formation, hydrothermal fluids activities, and silicon cycling in hydrosphere have been summarized. Compared to the thermodynamic isotope fractionation of silicon associated with high-temperature processes, that in low-temperature geological processes is much more significant (e.g., chemical weathering, biogenic/non-biogenic precipitation, biological uptake, adsorption, etc.). The equilibrium silicon isotope fractionation during the mantle-core differentiation resulted in the observed heavy isotope composition of the bulk silicate Earth (BSE). The equilibrium fractionation of silicon isotopes among silicate minerals are sensitive to the Si–O bond length, Si coordination numbers (CN), the polymerization degrees of silicate unites, and the electronegativity of cations in minerals. The preferential enrichment of different speciation of dissoluble Si (DSi) (e.g., silicic acid H4SiO40 (H4) and H3SiO4− (H3)) in silica precipitation and diagenesis, and chemical weathering, lead to predominately positive Si isotope signatures in continental surface waters, in which the dynamic fractionation of silicon isotope could be well described by the Rayleigh fractionation model. The role of complexation in biological fractionations of silicon isotopes is more complicated, likely involving several enzymatic processes and active transport proteins. The integrated understanding greatly strengthens the potential of δ30Si proxy for reconstructing the paleo terrestrial and oceanic environments, and exploring the meteorites and planetary core formation, as well as constraining ore deposits and hydrothermal fluid activity.

Calcium Isotope Fractionation During Mineral Precipitation from Aqueous Solution

Calcium Stable Isotope Geochemistry - Advances in Isotope Geochemistry ◽

10.1007/978-3-540-68953-9_3 ◽

2016 ◽

pp. 75-110 ◽

Cited By ~ 4

Author(s):

Nikolaus Gussone ◽

Martin Dietzel

Keyword(s):

Aqueous Solution ◽

Isotope Fractionation ◽

Calcium Isotope ◽

Mineral Precipitation

Naturally Occurring Stable Calcium Isotope Ratios in Body Compartments Provide a Novel Biomarker of Bone Mineral Balance in Children and Young Adults

Journal of Bone and Mineral Research ◽

10.1002/jbmr.4158 ◽

2020 ◽

Author(s):

Rukshana Shroff ◽

Mary Fewtrell ◽

Alexander Heuser ◽

Ana Kolevica ◽

Alexander Lalayiannis ◽

...

Keyword(s):

Young Adults ◽

Bone Mineral ◽

Isotope Ratios ◽

Calcium Isotope ◽

Mineral Balance ◽

Naturally Occurring ◽

Children And Young Adults ◽

Body Compartments ◽

Stable Calcium

Potassium isotope fractionation during chemical weathering of basalts

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2020.116192 ◽

2020 ◽

Vol 539 ◽

pp. 116192 ◽

Cited By ~ 3

Author(s):

Heng Chen ◽

Xiao-Ming Liu ◽

Kun Wang

Keyword(s):

Chemical Weathering ◽

Isotope Fractionation

Calcium isotope fractionation during coccolith formation inEmiliania huxleyi:Independence of growth and calcification rate

Geochemistry Geophysics Geosystems ◽

10.1029/2006gc001422 ◽

2007 ◽

Vol 8 (5) ◽

pp. n/a-n/a ◽

Cited By ~ 50

Author(s):

Gerald Langer ◽

Nikolaus Gussone ◽

Gernot Nehrke ◽

Ulf Riebesell ◽

Anton Eisenhauer ◽

...

Keyword(s):

Isotope Fractionation ◽

Calcium Isotope ◽

Calcification Rate