On the occurrence of jahnsite/whiteite phases on Mars: A thermodynamic study
- 1 September 2022
- journal article
- research article
- Published by Mineralogical Society of America in American Mineralogist: Journal of Earth and Planetary Materials
- Vol. 107 (9), 1807-1817
- https://doi.org/10.2138/am-2022-8174
Abstract
Jahnsites/whiteites are a large family of phosphate hydrate minerals of relevance to terrestrial and martian mineralogy. It was recently hypothesized as being present in Gale Crater sediments from XRD analyses performed by the CheMin analyzer aboard the Curiosity rover. However, the conditions of formation and thermodynamic properties of these compounds are essentially unknown. In this work, we have optimized the ThermAP predictive thermodynamic approach to the analysis of these phases, allowing us to estimate for the first time the standard formation enthalpy (Delta H-f degrees), Gibbs free energy (Delta G(f)degrees), and entropy (S degrees) of 15 jahnsite/whiteite end-member compositions, as well as of related phases such as segelerite and alluaudites. These estimations were then used to feed speciation/phase diagram calculation tools to evaluate the relative ease of formation and stability of these hydrated minerals, including considering present martian conditions. Selected laboratory experiments confirmed calculation outcomes. All of our data suggest that the formation of jahnsites is an unlikely process, and point instead to the formation of other simpler phosphate compounds. The stability domain, as calculated here, also raises serious questions about the possible presence of jahnsites on Mars as in Gale Crater, which appears rather improbable.Keywords
This publication has 28 references indexed in Scilit:
- A comprehensive guide to experimental and predicted thermodynamic properties of phosphate apatite minerals in view of applicative purposesThe Journal of Chemical Thermodynamics, 2015
- Equations for calculating hydrogeochemical reactions of minerals and gases such as CO2 at high pressures and temperaturesGeochimica et Cosmochimica Acta, 2014
- Crystal structure of whiteite-(CaFeMg) from Crosscut Creek, CanadaZeitschrift für Kristallographie, 2011
- Jahnsite—whiteite solid solutions and associated minerals in the phosphate pegmatite at Hagendorf-Süd, Bavaria, GermanyMineralogical Magazine, 2010
- Estimating the thermodynamic properties of phosphate minerals at high and low temperature from the sum of constituent unitsEstudios Geológicos, 2009
- Jahnsite-(NaFeMg), a new mineral from the Tip Top mine, Custer County, South Dakota: Description and crystal structureAmerican Mineralogist: Journal of Earth and Planetary Materials, 2008
- Mineralogy and chemistry of urinary stones: patients from North JordanEnvironmental Geochemistry and Health, 2007
- Jarosite stability on MarsIcarus, 2005
- Synthesis, characterization, and thermochemistry of K-Na-H3O jarositesGeochimica et Cosmochimica Acta, 2003
- Thermochemical Properties of PhosphatesPublished by Springer Science and Business Media LLC ,1984