The barite studied in the Villamayor sandstone is located in old rhizoliths related to subvertical fractures which affect these subarcosic deposits. These zones are actually in great circulation within underground waters and full of clay materials. The mineral's form together with ist mineralogical, chemical and isotopic characteristics suggests that its formation is related with the postneogene alteration processes (caolinitization) of sandstones which liberate Ba of the feldspars and with the infiltration and circulation of metheoric waters that contain dissolved sulphates