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 (ΔHfo⁠), Gibbs free energy (ΔGfo⁠), 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 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.

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关于火星上 jahnsite/whiteite 相的发生：一项热力学研究

Jahnsites/whiteites 是与陆地和火星矿物学相关的一大类磷酸盐水合物矿物。根据好奇号火星车上的 CheMin 分析仪进行的 XRD 分析，最近假设它存在于盖尔陨石坑沉积物中。然而，这些化合物的形成条件和热力学性质基本上是未知的。在这项工作中，我们优化了分析这些相的 ThermAP 预测热力学方法，使我们能够首次估计标准形成焓 (ΔHfo)、吉布斯自由能 (ΔGfo) 和熵 (S°) 15 种 jahnsite/whiteite 端元成分，以及相关相，如 segelerite 和 alluaudites。然后将这些估计用于提供物种形成/相图计算工具，以评估这些水合矿物的相对容易形成和稳定性，包括考虑目前的火星条件。选定的实验室实验证实了计算结果。我们所有的数据都表明 jahnsites 的形成是一个不太可能的过程，而是指向其他更简单的磷酸盐化合物的形成。在这里计算的稳定性域也提出了关于火星上可能存在的 jahnsite 的严重问题，就像在盖尔陨石坑中一样，这似乎不太可能。而是指向其他更简单的磷酸盐化合物的形成。在这里计算的稳定性域也提出了关于火星上可能存在的 jahnsite 的严重问题，就像在盖尔陨石坑中一样，这似乎不太可能。而是指向其他更简单的磷酸盐化合物的形成。在这里计算的稳定性域也提出了关于火星上可能存在的 jahnsite 的严重问题，就像在盖尔陨石坑中一样，这似乎不太可能。