Abstract The formation of kaolinite-smectite mixed-layered clays results from weathering of smectite in leached and silica-depleted environments. Halloysite-smectite mixed-layered clays have been proposed to form from weatherable minerals in volcanic ash soils through simultaneous formation of 1:1 and 2:1 units in silica-rich environments. Here, we report a mineralogical study of weathered B horizon material from soils developed on Late Quaternary fluvio-volcanic deposits of basaltic origin at the southern foot of Mount Kilimanjaro in northern Tanzania. This area is characterized by a strong seasonality: two months of highly humid conditions followed by a 10-month pronounced dry season during which mineral authigenesis takes place. The weak leaching conditions are reflected in the high base saturation of the soils and by their high content of amorphous silica. The soils contain no allophane. The clay fractions contain dioctahedral 1:1 layer silicates, trioctahedral mica, gibbsite and feldspar, as well as a substantial amount of 1:1/2:1 mixed-layered clays with predominance of 1:1 layers. The latter consist of dehydrated halloysite that only partially expands after formamide intercalation, because of its history of drying in field conditions. The interstratified phases are high-charge halloysite-smectite mixed-layered clays (CEC 30–72 cmol(+) kg−1 clay) that are predominantly very fine grained (

中文翻译：

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坦桑尼亚乞力马扎罗山南麓河流火山土壤中埃洛石-蒙脱石混合层状粘土

摘要 高岭石-蒙脱石混合层状粘土的形成是蒙脱石在浸出和贫硅环境中风化的结果。已提出埃洛石-蒙脱石混合层状粘土由火山灰土壤中的耐候矿物通过在富含二氧化硅的环境中同时形成 1:1 和 2:1 单元而形成。在这里，我们报告了对来自坦桑尼亚北部乞力马扎罗山南麓玄武岩起源的晚第四纪河流火山沉积物的土壤风化 B 层材料的矿物学研究。该地区的特点是季节性强：两个月的高湿条件，然后是长达 10 个月的明显旱季，在此期间发生矿物自生。弱浸出条件反映在土壤的高碱饱和度和高含量的无定形二氧化硅上。土壤中不含水溶脂。粘土组分包含二八面体 1:1 层状硅酸盐、三八面体云母、三水铝石和长石，以及大量 1:1/2:1 混合层状粘土，主要为 1:1 层。后者由脱水埃洛石组成，由于其在田间条件下干燥的历史，因此在甲酰胺嵌入后仅部分膨胀。层间相是高电荷埃洛石-蒙脱石混合层状粘土（CEC 30-72 cmol(+) kg-1 粘土），主要是非常细粒的（以及大量 1:1/2:1 混合层状粘土，其中 1:1 层占优势。后者由脱水埃洛石组成，由于其在田间条件下干燥的历史，因此在甲酰胺嵌入后仅部分膨胀。层间相是高电荷埃洛石-蒙脱石混合层状粘土（CEC 30-72 cmol(+) kg-1 粘土），主要是非常细粒的（以及大量 1:1/2:1 混合层状粘土，其中 1:1 层占优势。后者由脱水埃洛石组成，由于其在田间条件下干燥的历史，因此在甲酰胺嵌入后仅部分膨胀。层间相是高电荷埃洛石-蒙脱石混合层状粘土（CEC 30-72 cmol(+) kg-1 粘土），主要是非常细粒的（