Soils mineralogy of the Guadarrama ridge. Madrid. Spain

Abstract

The mineralogy of fine sand (light and heavy fractions) and clay fractions of different soils are studied. The soils are distric, eutric, umbric y mollic Leptosols; distric and eutric Cambisols; haplic Luvisols and haplic Phaeozems (FAO 1998) in the Guadarrama ridge (Morcuera, Navafría and Cerro de la Cruz-El Chaparral) developed from gland gneiss and under different vegetation: shrublands of Cytisus oromediterraneus-Genista florida on Morcuera Port and Navafria Port, Quercus pyrenaica forest (in Morcuera) and Pinus sylvestris forest (in Navafría) on the middle slope and meadows on the valleys; on Cerro de la Cruz-El Chaparral there is a mixed woodland of Juniperus oxycedrus, Quercus ilex and Juniperus thuriphera. The climate of the study area is fresh temperate mediterranean , with 895 mm of precipitation and the mean annual temperature is 10.1 ºC. In this study, we used polarization microscopy to identify the heavy minerals of the fine sand and X-ray diffraction to identify the light minerals of fine sand and the clay minerals. Loamy sand and sandy loam is the most common textural class in these soils. The light fraction of fine sand, the main mineralogical fraction of this soils, is constituted by quartz, feldespars and micas, this mineralogical assemblage also defines the mineralogical composition of parent material, gneiss. In the scarce heavy fraction of the fine sand micaceus minerals (mainly biotite and muscovite), metamorphic minerals (sillimanite, staurolite and garnet) and stable minerals (zircon and tourmaline) point out the same parent material, gneiss.The soils are autocthons.The inheritance and transformation processes are the origin of soil clays: illite, vermiculite, kaolinite and interlayered minerals like: micas-vermiculites, chlorite-vemiculite and micas-chlorite.