The Amazonia Forest is an important biome that possess a great diversity of fauna and flora which can play a significant role in several areas of science, specially, the gene reserve for the future of mankind. At the same time, it is a very poorly understood environment, particularly the basis of this ecosystem, its soils. This study was conducted to gain insight in the mineralogy of important soils classes of the Amazonia sedimentary basin. The soils in the upland position in the landscape are developed from tertiary sediments belonging to the Alter do Chão series and those in the floodplain position are derived from quaternary, more specifically, holocene´s sediments.

Sand, silt and clay fractions were separated and X-ray diffraction analysis was conducted. Very simple mineralogy composed basically of quartz in the coarser fractions and kaolinite, goethite and anatase for the finer fraction was found for the Oxisol, the Ultisol and the Entisol from an upland toposequence but differences in kaolinite crystallography could be noticed among them. Gibbsite was virtually absent, in spite of the advanced degree of development of most of these soils.

More distinctive mineralogy was revealed for the soils developed in the more recent sediments with quartz and feldspars in the sand and silt fractions and a suite of 2:1 minerals also appearing in their clay fraction, besides kaolinite and goethite.

In one upland soil petroplinthite is the main feature and its mineralogy reflected its environment of formation which is usually associated with level to gently sloping areas with fluctuating  water table.

There is a clear differentiation between the mineralogy of the upland and the flood plain position soils as the result of the advancement of the soil formation in these two environmental compartments which reflects in the different use and management of the soils.