Chemical and mineralogical characterization of soils derived from ophites in Mediterranean climate (North of Spain)

We have studied the chemical and mineralogical characteristics of ophites l ocated in a diapiric formation in Burgos (North of Spain), and the soils de rived from them. The ophites studied show mineralogical uniformity. Their m ain components are clinopyroxenes, plagioclases, biotite, and olivine. Gene rally, they show deuteric alteration mainly affecting the olivine. The pres ence of talc is attributed to an outpouring of basic magma (ophite) in an e vapotiric environment of Keuper facies. Chemically, they are basic rocks, o f basaltic nature, poor in silicon dioxide (SiO2) and rich in magnesium oxi de (MgO) and ferric oxides (Fe2O3). The weathering of the ophites results i n clay consisting of chlorite, vermiculite, and interlayer chlorite-vermicu lite-smectite inherited from original material. Small amount of extractable silica (Si), aluminum (Al), and iron (Fe) show the scarcity of amorphous m aterial attributed to the high content in organic carbon (C) which prevents formation of allophane, and to the xeric moisture regime of soils in this location.