Nature and Properties of the Soils of the Red and Black Complex of the Hawaiian Islands

Abstract

A study was made of the mineralogical constitution of the soils of the red and black complex of the Hawaiian Islands. The application of differential thermal analysis established kaolin as the dominant mineral in the red soils and montmorillonite as the dominant mineral in the black soils. To aid in the understanding and interpretation of the experimental data a discussion of the differential thermal apparatus and the clay minerals was given. Four major variations in the soils of the red and black complex, differing in modes of formation, were recognized. The first type consists of black soils forming under low rainfall at low elevations adjacent to red soils forming under higher rainfall on upper elevations. Type II black soils may form under heavier rainfall than type I, but are stabilized by seepage waters from adjacent red soils. Type III comprises a number of black soils developing under restricted drainage, as a result of a high water table, near red soils having better internal drainage. Type IV consists of several profiles of alluvial and ash material, where a red top soil rests upon a black subsoil. In every case, except in a red and black profile from Molokai, kaolin was found to be the dominant clay mineral in the red soil and montmorillonite in the black soil, with a kaolin montmorillonite mixture in the transitionary zones. Under intense leaching and oxidation, kaolin formation was favored. In situations where retention of bases and silica was favored, montmorillonite formation occurred. The cause for the soil colors was reviewed. Hematite and goethite were listed as the main cause for the color in the red soils. Investigation of black soils low in organic carbon from Kunia road supports the view that the black color need not necessarily be associated with organic matter.