Understanding the behavior of secondary minerals under alkaline conditions is important for predicting the potential alteration of the constituent minerals in radioactive-waste disposal facilities. A previous study reported the formation of uncommon Fe- and Mg-bearing clays under natural alkaline conditions in the Philippines; these were referred to as iron-magnesium-silicate-hydrates (F-M-S-H) and nontronite-like minerals. The current study aimed to investigate the structural and chemical characteristics and to understand the formation pathways of these clays by performing a detailed characterization. F-M-S-H comprised tetrahedral–octahedral–tetrahedral (TOT) layers, imperfect interlayer hydroxide sheets, and interlayer Ca ions. The systematic changes in the characteristics of F-M-S-H at different sampling depths, such as the gradual decrease of the interlayer hydroxide sheets to form smectitic domains, were caused by the differing interaction periods between each sediment at different sampling depths and alkaline seepage. Furthermore, F-M-S-H was ferrous in form prior to oxidation. In contrast, a nontronite-like mineral comprised nontronite and part of an interlayer hydroxide sheet. This mineral was inferred to be formed under chemically different conditions from F-M-S-H, and probably formed in the presence of aqueous Fe³⁺ and Mg ions.

了解碱性条件下次生矿物的行为对于预测放射性废物处理设施中组成矿物的潜在变化非常重要。先前的一项研究报告了菲律宾在天然碱性条件下形成了罕见的含铁和镁的粘土；这些被称为铁镁硅酸盐水合物（FMSH）和类绿脱石矿物。目前的研究旨在调查结构和化学特征，并通过进行详细的表征来了解这些粘土的形成途径。FMSH 由四面体-八面体-四面体 (TOT) 层、不完美的层间氢氧化物片和层间 Ca 离子组成。不同采样深度下FMSH特征的系统变化，如层间氢氧化物片逐渐减少形成蒙脱石域，是由于不同采样深度的沉积物之间的不同相互作用周期和碱性渗流造成的。此外，FMSH 在氧化前呈亚铁形态。相反，类绿脱石矿物包含绿脱石和夹层氢氧化物片的一部分。推测这种矿物是在与 FMSH 不同的化学条件下形成的，可能是在 Fe 水溶液的存在下形成的 一种绿脱石类矿物，包括绿脱石和层间氢氧化物片的一部分。推测这种矿物是在与 FMSH 不同的化学条件下形成的，可能是在 Fe 水溶液的存在下形成的 一种绿脱石类矿物，包括绿脱石和层间氢氧化物片的一部分。推测这种矿物是在与 FMSH 不同的化学条件下形成的，可能是在 Fe 水溶液的存在下形成的³⁺和 Mg 离子。