The Reference Soil Group of the Durisols is represented in arid and semi-arid environments and holds very shallow to moderately deep, free-draining soils 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).

Durisols are confined to dry regions, where they occur in association with Gypsisols, Calcisols, Solonchaks, Solonetz, Vertisols, Arenosols, Cambisols and, more rarely, Planosols or Kastanozems. In places, Durisols occur together with Andosols. In areas with silica-capped mesas, Durisols may be found in lower parts of the landscape.

Most Durisols occur in strongly weathered alluvial or colluvial parent material. It is generally believed that duric and petroduric horizons form by downward translocation of clay and silica, even in regions with a very low annual rainfall sum. Periodic flooding and wetting of the surface soil during occasional heavy downpours promote leaching and acidification of the upper soil layer; the leached silica accumulates deeper in the soil where it hardens as the soil dries out.

The consistent occurrence of a cemented hardpan (a petroduric horizon, often referred to as a `duripan') at shallow depth, even beneath surfaces on which new soil material regularly accumulates, is accepted as evidence that silica translocation is still taking place. The consistent positive correlation between the depth of the hardpan and the permeability of the overlying soil is a further indication that hardpan formation is not a paleo-feature.