Clay mineralogy of a Dystrandept and a Haplaquod from Northland, New Zealand

Abstract

Two soil sampies (Ap1 and Bw3 horizons) from a Dystrandept (Papakauri) developed on basaltic scoria and two sampies (Bh1 and Bs2 horizons) from a Haplaquod (One Tree Point) on dune sands, Northland, New Zealand were analysed for their clay mineral composition by a combination of mt!thods. Absence of allophane was confirmed in the Papakauri Dystrandept. Instead, hydrous alumina and allophane-Iike constituents contributed to the “andic” nature of the soH. Predominance of allophane in the Bs2 horizon clay of the One Tree Point Haplaquod, but existence of lower amounts of this constituent (20% at most) in the Bhl horizon clay was interpreted as an indication that the continued supply of the complexing organic matter from the overlying horizons suppresses the formation of allophane. The abundance of volcanic glass in the fine sand from the Haplaquod indicated that the major parent materials were finely comminuted volcanic ejecta which primarily contributed 10 the formation of the non-crystalline clay constituents in the soil.