This thesis describes the research work done on the mineralogy and properties of iron oxides in a weathered granite from Hong Kong Island. In general, after the initial introductory chapters, subsequent chapters present studies made using different techniques with one chapter discussing one technique. Chapter 1 gives the Introduction to the research and presents a basis for the study as well as the aim of the research. The methodology used in accomplishing the aims is presented. Chapter 2 reviews the past literature relating to the investigation. The structure of the different iron oxides as proposed by past workers as well as the occurence, properties and characteristics of iron oxides in the soil environment are reviewed. In Chapter 3 descriptions of the soil materials are given in order to provide a framework of reference for the main part of the work. The sampling methods and both the field and laboratory descriptions of the soils used in the study are provided together with a brief geology of the sampling site. The initial sample preparation done prior to testing the soils has been outlined and results of preliminary tests such as particle size analysis and scanning electron microscopy presented. Chapter 4 presents the aspect of the investigation where wet chemistry was used to provide additional information which helped in explaining some of the observation of the main techniques used. The chemical tests perfomed included concentration methods for the iron oxides using the 5 M boiling NaOH and HF methods, selective dissolution using dithionite citrate bicarbonate and acid ammonium oxalate methods, and determination of the chemical contents of the untreated soils and residues obtained from the different treatments. pH and organic content determination of the soils were also performed. Chapter 5 presents the electron microscopy study on the different fractions of the soils. The method has the advantage of allowing direct observation of the particles being studied. The theories explaining the acquisition of images in the transmission electron microscope are included. The experimental methods used for transmission and scanning electron microscopy are also presented. Complementary results of scanning electron microscopy are also given. The clay minerals and iron oxide minerals were identified on the basis of data provided by electron diffraction and lattice images, and the morphology of the different minerals is described. Chapter 6 presents X--- ray diffraction analysis on the samples. The technique complements electron microscopy in the identification of the mineralogy of the various soil components. Furthermore X-ray diffraction made it possible to estimate Al substitution for Fe in the iron oxide structure, a property that helped in explaining the formation and occurence of the iron oxides in the soils. The experimental technique and testing procedures are given and the results presented and discussed. Chapter 7 gives the details of the infrared spectroscopy and differential scanning calorimetery study of the soils. Both methods allowed a study of the mineralogy of the clays and iron oxides in the soils, thereby complementing the work done using electron microscopy and X-ray diffraction. Some additional information on particle size of some of the clay minerals was also obtained. The characteristics of the infrared vibrations and DSC traces of the iron oxides have been explained on the basis of some peculiar properties of the oxides. Chapter 8 presents a general discussion on the basis of the collective results obtained from using the different analytical techniques. The chapter also serves as a summary for some of the results presented earlier in the different chapters. Important conclusions drawn from these results are presented and discussed