¹Christophe Drouet,²Matteo Loche,²Sébastien Fabre,²Pierre-Yves Meslin
American Mineralogist 107, 1807-1817 Link to Article [http://www.minsocam.org/MSA/AmMin/TOC/2022/Abstracts/AM107P1807.pdf]
¹CIRIMAT, Université de Toulouse, CNRS, Toulouse INP, UPS, 4 allée Emile Monso, 31030 Toulouse, France
²Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, UPS, CNRS, CNES, 9 Avenue du Colonel Roche, 31400 Toulouse, France
Copyright: The Mineralogical Society of America

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 (ΔHf°), Gibbs free energy
(ΔGf°), and entropy (S°) 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 calcula-
tion 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.

^1,2Niccolò Satta,³Masaaki Miyahara,⁴Shin Ozawa,²Hauke Marquardt,⁵Masahiko Nishijima,⁶Tomoko Arai,⁴Eiji Ohtani
American Mineralogist 107, 1661-1667 Link to Article [http://www.minsocam.org/MSA/AmMin/TOC/2022/Abstracts/AM107P1661.pdf]

¹Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth 95440, Germany
²Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, U.K.
³Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
⁴Department of Earth Science, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
⁵Laboratory for Protein Crystallography and Laboratory for Electron Structural Biology Institute for Protein Research, Osaka University, Suita-shi Osaka 565-0871, Japan
⁶Planetary Exploration Research Center, Chiba Institute of Technology, Chiba 275-0016, Japan
Copyright: The Mineralogical Society of America

The Apollo 15 mission returned various samples of regolith breccias, typical lunar rocks lithified
by impact events on the Moon’s surface. Here we report our observations on shock features recorded
in a section of the Apollo Sample 15299. We observe the presence of ferropericlase crystals confined
in a shock-melt pocket and conclude that their formation is related to a shock-induced incongruent
melting of olivine. While predicted by experiments, this phenomenon has never been observed in a
natural sample. The incongruent melting of olivine provides an important signature of melting under
high-pressure conditions and allows for estimating the pressure-temperature (P-T) experienced by the
studied sample during the impact event. We infer that the fracture porosity that likely characterized the
studied sample prior to the shock event critically affected the P-T path during the shock compression
and allowed the studied sample to be subjected to elevated temperature during relatively low shock
pressures.