Characterization of loess in central Spain: a microstructural study

The purpose of this paper is to characterize the materials developed in the middle Tajo River valley, Central Spain. These sediments are loess, the characterization of which has not been reported in the international bibliography. The sediments are related to the next geological context and their characterization is indispensable to locate the said material in the adequate environment. A few different methods have been employed in this study, such as the pipette method (for determining the grain size) and separation of the light and heavy minerals of the sand fraction by using bromoform. The mineralogical composition was determined by XRD and textural study was accomplished by SEM/EDX. The loessic materials are silt-clay or sandy-silt that are quite unstable. The mineralogical composition shows quartz, feldspar, calcite and clay minerals. Some samples show gypsum; this mineral and calcite present dissolution and stability problems. The heavy minerals starting from the sand fraction are tourmaline, zircon, garnet, staurolite, sillimanite and biotite associations. The studies carried out with SEM show that the quartz grain surfaces present etch pits typical of the wind-blown origin.