Evaluation of letsoku and related Southern African indigenous clayey soils

Abstract

The nature of letsoku and related clayey soils, traditionally used by indigenous Southern African communities for a wide range of purposes, was explored. Thirty-nine samples were collected from Botswana, Lesotho, Swaziland, South Africa and Zimbabwe. They were analysed to determine their composition and physical properties. Structured interviews were used to establish the purpose of use and the location of sourcing sites. The samples were in the form of either powder or rocks, and some were supplied as dry rolled clay balls. Cosmetic applications were almost universally indicated. However, other functions, related to artwork, medicinal use, cultural symbolism and traditional beliefs, were also mentioned. The samples covered a wide range of colours from bright red to yellow, but also from off-white to black, with some having a light grey colour. It was therefore not surprising that the mineral composition of the letsoku samples also varied widely. A black sample, and the yellow and reddish pastel-coloured samples, contained significant quantities of the corresponding, colourimparting iron oxides. Clay minerals featured prominently, although kaolinite and muscovite were more often encountered as the dominant minerals than smectites. All the samples contained silica and in some instances the content exceeded 90 % m/m SiO2. The presence of high contents (more than 40 % m/m) of gibbsite in the samples from Venda represents a new finding for clayey soils in traditional usage.