Abstract Praseodymium is capable of existing as Pr3+ and Pr4+. Although the former is dominant across almost all geological conditions, the observation of Pr4+ by XANES and Pr anomalies (both positive and negative) in multiple light rare earth element minerals from Nolans Bore, Australia, and Stetind, Norway, indicates that quadrivalent Pr can occur under oxidizing hydrothermal and supergene conditions. High-temperature REE partitioning experiments at oxygen fugacities up to more than 12 log units more oxidizing than the fayalite-magnetite-quartz buffer show negligible evidence for Pr4+ in zircon, indicating that Pr likely remains as Pr3+ under all magmatic conditions. Synthetic Pr4+-bearing zircons in the pigment industry form under unique conditions, which are not attained in natural systems. Quadrivalent Pr in solutions has an extremely short lifetime, but may be sufficient to cause anomalous Pr in solids. Because the same conditions that favor Pr4+ also stabilize Ce4+ to a greater extent, these two cations have similar ionic radii, and Ce is more than six times as abundant as Pr, it seems that Pr-dominant minerals must be exceptionally rare if they occur at all. We identify cold, alkaline, and oxidizing environments such as oxyhalide-rich regions at the Atacama Desert or on Mars as candidates for the existence of Pr-dominant minerals.

中文翻译：

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行星材料中的四价镨

摘要 镨能够以Pr3+和Pr4+的形式存在。尽管前者在几乎所有地质条件下都占主导地位，但 XANES 对 Pr4+ 的观察和来自澳大利亚 Nolans Bore 和挪威 Stetind 的多种轻稀土元素矿物中的 Pr4+ 和 Pr 异常（正负）表明，四价 Pr 可以发生在氧化性热液和表生条件下。在氧逸度比铁橄榄石-磁铁矿-石英缓冲液氧化性高 12 log 单位以上的高温 REE 分配实验显示，锆石中 Pr4+ 的证据可以忽略不计，表明在所有岩浆条件下，Pr 可能仍为 Pr3+。颜料工业中的合成 Pr4+ 锆石是在独特的条件下形成的，这在自然系统中是无法实现的。溶液中的四价 Pr 寿命极短，但可能足以在固体中引起异常 Pr。因为同样有利于 Pr4+ 的条件也更大程度地稳定了 Ce4+，这两种阳离子具有相似的离子半径，而且 Ce 的含量是 Pr 的 6 倍以上，看来 Pr 主导的矿物如果出现在全部。我们将阿塔卡马沙漠或火星上富含卤氧化物的寒冷、碱性和氧化环境确定为存在 Pr 主导矿物的候选者。看来，以 Pr 为主的矿物如果真的出现的话，一定是非常罕见的。我们将阿塔卡马沙漠或火星上富含卤氧化物的寒冷、碱性和氧化环境确定为存在 Pr 主导矿物的候选者。看来，以 Pr 为主的矿物如果真的出现的话，一定是非常罕见的。我们将阿塔卡马沙漠或火星上富含卤氧化物的寒冷、碱性和氧化环境确定为存在 Pr 主导矿物的候选者。