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 located in a diapiric formation in Burgos (North of Spain), and the soils derived from them. The ophites studied show mineralogical uniformity. Their main components are clinopyroxenes, plagioclases, biotite, and olivine. Generally, they show deuteric alteration mainly affecting the olivine. The presence of talc is attributed to an outpouring of basic magma (ophite) in an evapotiric environment of Keuper facies. Chemically, they are basic rocks, of basaltic nature, poor in silicon dioxide (SiO2) and rich in magnesium oxide (MgO) and ferric oxides (Fe2O3). The weathering of the ophites results in clay consisting of chlorite, vermiculite, and interlayer chlorite-vermiculite-smectite inherited from original material. Small amount of extractable silica (Si), aluminum (Al), and iron (Fe) show the scarcity of amorphous material 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.