What's in a name : laterite, plinthite, ferricrete, pedocrete, geocrete and duricrust - is there any difference, and is it of any engineering significance?

Abstract

Some of the English terminology used to describe the secondary, near-surface, ferruginous nodules, concretions, gravels and hardpans often found in the soil profile and used in pavement construction in southern Africa and elsewhere is briefly reviewed. Although the term ‘laterite’ (Latin: later, brick) has chronological priority and is globally the most common, it has become so widely used and misused as to be almost meaningless and has been replaced in pedology by the closely defined term ‘plinthite’ (Greek: plinthos, brick). For pavement and geotechnical purposes, the term ‘laterite’ should therefore be restricted to materials which comply with pavement material specifications specifically for laterite such as those of Brazil, which include the chemical and/or mineralogical criteria defining the materials from which the specifications were derived, and/or which possess self-hardening properties such as the laterites used for centuries as building blocks in India and adjacent countries. For pavement and geotechnical purposes, the term ‘ferricrete’ (i.e. soil particles cemented by iron oxide) most aptly describes these materials, which are apparently not usually self- hardening. Ferricrete is a member of the family of pedocretes or geocretes such as calcrete (soil particles cemented by calcite), silcrete (cemented by silica), etc., also called duricrusts. Pedocretes are formed by soil-forming processes in the pedological sense and geocretes by what some pedologists regard as geological processes. The origin and chemical and mineralogical composition of these ferruginous materials are briefly reviewed and their engineering significance discussed.