This paper summarizes available information on soil clay mineralogy in topsoils of Costa Rica, including clay minerals  described in B horizons when significantly different from predominant mineralogy in the topsoil. The soil clay suites (“predominant clay groups”) emphasized are grouped as: (1) smectites and interstratified clays (Vertisols and other soils with vertic properties), and (2) oxides-hidroxides oxihidroxides-kaolinite-gibbsite (in Alfisols, Ultisols and Oxisols). The soil clay genesis of these dominant groups is discussed when enough information is available.

Clay; soil; Vertisol; Alfisol; Ultisol; Oxisol; smectite; montmorrillonite; vermiculite; illite; halloysite; metahalloysite; chlorite; ferrihydrite; hematite; maghemite; magnetite; goethite; kaolinite; gibbsite; Costa Rica; tropic