Delvaux, B., Herbillon, AJ., & Vielvoye, L. (1989). Characterization of a Weathering Sequence of Soils Derived From Volcanic Ash in Cameroon - Taxonomic, Mineralogical and Agronomic Implications. Geoderma, 45(3-4), 375-388. https://doi.org/10.1016/0016-7061(89)90017-7 (Original work published 1989)