Mineral transformations in soils are important processes in assessing pedogenesis. A micromorphological study, complemented by mineralogical and physicochemical analyses, was conducted for two contrasting soils developed on tephra of Mt. Manengouba, i.e. an Andosol and a Cambisol, in order to compare weathering trends based on olivine and biotite alteration. The contrasting character of the two soils is portrayed in their various properties, and is also observed in the field. The majority of the investigated soil properties proved to be effective in capturing differences between the two soils. Iddingsite, formed by pellicular alteration of olivine, occurs in both soils. Its presence is an inherited feature, as recorded by identical occurrences of affected olivine crystals as isolated grains in the groundmass of the soils and as phenocrysts in volcanic rock fragments within the Andosol profile. Kaolinitisation of biotite, producing parallel linear alteration patterns, is limited to the Cambisol and is attributed to pedogenic processes, recording a more advanced stage of weathering than for the Andosol profile. Kaolinitisation is thus more indicative in assessing pedogenesis compared with iddingsitisation in these soils.

中文翻译：

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在喀麦隆火山线 (CVL) 沿线的两种不同的火山灰衍生土壤中橄榄石的识别和黑云母的高岭土化

土壤中的矿物转化是评估成土作用的重要过程。对在山的火山灰上开发的两种对比土壤进行了微形态研究，辅以矿物学和物理化学分析。Manengouba，即 Andosol 和 Cambisol，以比较基于橄榄石和黑云母蚀变的风化趋势。两种土壤的对比特征表现在它们的各种特性中，并且在现场也能观察到。大多数研究的土壤特性被证明在捕捉两种土壤之间的差异方面是有效的。Iddingsite 由橄榄石的表皮蚀变形成，在两种土壤中都存在。它的存在是一种遗传特征，据记录，受影响的橄榄石晶体作为土壤基质中的孤立颗粒和安多索剖面内火山岩碎片中的斑晶出现相同。黑云母的高岭土化，产生平行的线性蚀变模式，仅限于 Cambisol，归因于成土过程，记录了比 Andosol 剖面更高级的风化阶段。因此，与这些土壤中的 iddingsitisation 相比，高岭土化在评估成土作用方面更具指示性。