The kaolinite-to-chlorite conversion is one of the chloritization processes that occurs in low temperature diagenetic and hydrothermal systems. The mechanism of this mineralogical transformation is still under discussion, since direct transformation, conversion via berthierine as intermediate phase or direct formation of berthierine/chlorite mix, either by dissolution-crystallization or by solid state transformation (or a combination of both), are all hypotheses put forward. In this context, each description of a kaolinite-to-chlorite conversion occurrence becomes an opportunity to shed new light and to renew this debate. Studying Carboniferous shale–crosscut by large quartz-kaolinite veins–from the mining basin of the North of France, we report therefore an uncommon kaolinite-Fe-rich chlorite assemblage. This assemblage appears as a chlorite fringe 20 µm wide along the interfaces between the shale and the quartz-kaolinite veins. All petrographical, mineralogical and chemical data suggest that the Fe-chlorite results from the interaction between the shale, providing the Fe,Mg supply, and the Si,Al-rich veins, leading to the chloritization of the kaolinite at a small scale via at least one dissolution-recrystallisation step. High-resolution observations highlight that neoformed Fe-rich chlorite contains some 7Å isochemical layers, as relict of berthierine. Therefore, we advance that the conversion takes place either through the precipitation of berthierine following by a second step involving solid state berthierine-chlorite conversion, or through the direct precipitation of a chlorite-rich/berthierine-poor mix driven by the Fe/(Fe + Mg) ratio, at low temperature and in reducing conditions. The comparison of our data with the recent literature allows to prefer the second hypothesis.

中文翻译：

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从富硅、富铝流体源脉/富铁石炭纪页岩相互作用将高岭石转化为绿泥石

高岭石到亚氯酸盐的转化是发生在低温成岩和热液系统中的绿泥石化过程之一。这种矿物学转变的机制仍在讨论中，因为直接转变、通过作为中间相的 berthierine 转化或通过溶解结晶或固态转变（或两者的组合）直接形成 berthierine/亚氯酸盐混合物都是提出的假设。在这种情况下，对高岭石到绿泥石转化事件的每一次描述都成为阐明新观点和重新讨论这一争论的机会。研究来自法国北部采矿盆地的石炭纪页岩 - 由大型石英高岭石脉横切，因此我们报告了一种罕见的富含高岭石 - 铁的绿泥石组合。这种组合在页岩和石英-高岭石脉之间的界面上表现为 20 µm 宽的绿泥石边缘。所有岩相学、矿物学和化学数据表明，Fe-绿泥石是由提供 Fe、Mg 供应的页岩和富含 Si、Al 的脉之间的相互作用产生的，导致高岭石在小范围内发生绿泥石化。至少一个溶解-重结晶步骤。高分辨率观察表明，新形成的富铁绿泥石包含一些 7Å 的同化层，作为 berthierine 的残余物。因此，我们提出转化是通过在涉及固态 berthierine-亚氯酸盐转化的第二步之后通过 berthierine 沉淀，或通过由 Fe/(Fe) 驱动的富含亚氯酸盐/贫berthierine 的混合物的直接沉淀而发生的。 + Mg) 比，在低温和还原条件下。我们的数据与最近的文献的比较允许更喜欢第二个假设。