The formation conditions and stability fields of Fe-serpentines are still poorly understood in both terrestrial (natural or anthropic) and extraterrestrial environments. Knowledge of the effects of physical-chemical parameters on compositional and structural features of Fe-serpentines is lacking, and only a few thermodynamic parameters of these minerals are available in the literature. To fill these gaps, the synthesis of these minerals, while controlling all the physicochemical experimental parameters, was undertaken. Two hydrothermal syntheses were carried out at 90°C to investigate the effect of two different starting mineralogical mixtures on the nature of Fe-serpentines. The run products were identified by several analytical techniques (powder X-ray diffraction, transmission, and scanning electron microscopy). Berthierine crystals were synthesized from a starting mixture of kaolinite and metal iron. The berthierines synthesized show different morphologies and iron contents (~3–38 at.%). From a starting mineralogical mixture composed of quartz and metal iron, cronstedtite crystallizes. Most of the crystals are 1 M polytypes. Magnetite is always associated with both berthierine and cronstedtite. Lepidocrocite was observed only in the experiment with kaolinite. These experimental results demonstrated that Fe enrichment in serpentines depends on the silicate precursor (kaolinite or quartz) of the starting mixture. The results are also in agreement with the geochemical equilibrium predicted by thermodynamic modeling, i.e. the formation of berthierine and cronstedtite in association with magnetite at the expense of metal iron and silicates.

中文翻译：

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起始矿物混合物对 90°C 水热合成过程中获得的 Fe-蛇纹石性质的影响

在陆地（自然或人类）和外星环境中，对铁蛇纹石的形成条件和稳定性场仍知之甚少。缺乏关于物理化学参数对铁蛇纹石组成和结构特征影响的知识，文献中只有少数这些矿物的热力学参数可用。为了填补这些空白，在控制所有物理化学实验参数的同时，进行了这些矿物质的合成。在 90°C 下进行了两次水热合成，以研究两种不同的起始矿物混合物对铁蛇纹石性质的影响。运行产品通过几种分析技术（粉末 X 射线衍射、透射和扫描电子显微镜）进行鉴定。Berthierine 晶体由高岭石和金属铁的起始混合物合成。合成的 berthierines 显示出不同的形态和铁含量（~3-38 at.%）。从由石英和金属铁组成的起始矿物混合物中，Cronstedtite 结晶。大多数晶体是1M多型体。磁铁矿总是与 berthierine 和 cronstedtite 联系在一起。仅在高岭石实验中观察到纤铁矿。这些实验结果表明，蛇纹石中 Fe 的富集取决于起始混合物的硅酸盐前体（高岭石或石英）。结果也与热力学模型预测的地球化学平衡一致，即以金属铁和硅酸盐为代价，与磁铁矿相关联的 berthierine 和 cronstedtite 的形成。