a mineral soil horizon at least 30 cm (11.8 in) thick and characterized by the virtual absence of weatherable primary minerals or 2:1 layer silicate clays, the presence of 1:1 layer silicate clays and highly insoluble minerals such as quartz sand, the presence of hydrated oxides of iron and aluminum, the absence of water dispersible clay and the presence of low cation exchange capacity, and the presence of small amounts of exchangeable basesThis definition last updated 07/22/2008