andique

CONT: andic = horizons containing significant amounts of allophane, imogolite, ferrihydrite or aluminum-humus complexes. That is, soils derived from volcanic ash. Pragmatically, these horizons have low bulk densities (e.g. 0.9 g/cm3), contain volcanic glass, and are thixotropic (particles readily re-arrange when wet and physically disturbed.)
CONT: Ando soils originating from volcanic ash are ... characterized by thick black A horizons, high values of organic carbon contents and high degrees of humification of soil humic acids.