High Quality Content by WIKIPEDIA articles! A Durisol in the FAO World Reference Base for Soil Resources is a very shallow to moderately deep, free-draining soil of arid and semi-arid environments, that contain cemented secondary silica (SiO2) in the upper metre of soil. Durisols are internationally known as "hardpan soils" (Australia) or "dorbank" (South Africa) or they represent the "duripan phase" of other soils, e.g. of Calcisols (FAO).