Study on Kaolinitization of Soil Clays

对泰国40个剖面的旱地土壤和河流沉积物样品进行了化学物理特性和矿物学研究。土壤一般是强酸性的。交换性盐基和有机质含量普遍较低。土壤质地差异很大，从砂质到粘土，剖面取决于母质的类型。粘土含量在每个剖面中向下增加，可能是由于幻化作用以及表面粘土的流失所致。与温带土壤相比，粉砂的含量普遍很低，表明其在热带土壤中具有暂时性。水浸提物中的微量营养物质如锌、铜、钼、锰的潜在含量普遍较低。除相对年轻的土壤和玄武岩发育的土壤外，砂土和粉砂均为石英质。前者含有相当数量的长石等风化矿物，后者含有赤铁矿和石英，被认为是受母质熔岩污染的包裹体的继承物。粘土几乎是高岭石，只有高岭石，高岭石+高岭石/蒙脱石混合层，或高岭石+埃洛石和/或三水铝石。高岭石/蒙皂石矿物被认为是蒙脱石高岭土进一步高岭化作用的产物。埃洛石被认为是高岭石在干燥土壤水分条件下转化的产物。辅助成分最丰富的是游离氧化铁，主要由赤铁矿和少量针铁矿组成。大多数土壤中含有一定数量的伊利石、蛭石和绿泥石。河流沉积物中除高岭石外，还含有大量的蛭石和伊利石。低地土壤中2：1型矿物含量高的原因可能是这种物质通过洪涝作用被掺入土壤中。

Samples from 40 profiles of upland soils and river sediments from Thailand were investigated for chemical and physical characteristics and mineralogy. The soils were generally strongly acid. The contents of exchangeable bases and organic matter were generally low. Soil texture varied widely, from sandy to clayey, with profiles depending on the type of parent materials. The clay content increased downward in each profile probably as a result of illuviation as well as loss of clays from the surface by run-off. The content of silt was generally very low as compared with the temperate soils, indicating its transient nature in the tropical soils.The potential contents of micro-nutrients, such as Zu, Cu, Mo, and Mn, were low in general as extracted by aqua regia.The sands and silts were entirely quartziferous, except for those from relatively young soils and from basaltic lave-derived soils. The former contained weatherable minerals such as feldspars in measurable quantities and the latter, hematite in addition to quartz which was considered as a inheritance from xenocrysts contaminated in the parent lava.The clays were almost kaolinitic, with kaolinite alone, kaolinite plus kaolinite/smectite mixed layers, or kaolinite plus halloysite and/or gibbsite. The kaolinite/smectite mineral was considered as a product of far-advanced stage of kaolinitization from smectite. The halloysite was considered as a product of transformation from kaolinite in a dry soil moisture regime. Most abundant of the accessory components were free iron oxides which consisted mostly of hematite with some goethite. Illite, vermiculite, and chlorite were recognized in certain amounts in most soils.The river sediments contained large amounts of vermiculite and illite, in addition to kaolinite. High contents of 2 : 1 type minerals in the lowland soils may be accounted for by incorporation of such materials by flooding.