Clay mineralogy of the B horizons of two hydrandepts, a Torrox and a Humitropept in Hawaii

Abstract

The mineralogy of the clay fractions separated from the B horizons of two Hydrandepts (Hilo and Akaka soils), a Torrox (Molokai soil) and a Humitropept (Kolekole soil) was determined by a combination of methods. The Hydrandept B horizons were characterized by predominance of hydrous non-crystalline alumina and iron oxides associated with considerable amounts of humus and with very small amounts of silica. Allophane, allophane-like constituents and imogolite were present but in minor amounts. Gibbsite, goethite, chlorite and illite were also present as accessory minerals. The Torrox and Humitropept B horizons were characterized by predominance of kaolinite, hematite and goethite. The iron oxide minerals were present as fine particles (40–80 A diameter) often clustered to form larger aggregates. Neither imogolite nor allophane and allophane-like constituents were detected. Considerable amounts of dithionite-citrate soluble Al and humus were, however, present in the Humitropept B horizon, which may reflect the effect of an admixture of volcanic ash to the parent material.