Physico-chemical and mineralogical characterisation of earthy materials indigenously used as cosmetics

Abstract

Africa is endowed with various earthy materials, of which each community is uniquely identified. Inspite of the vast knowledge of western cosmetics, application of traditionally used cosmetics have been in existence and will be into practice from generation to generation, this is as a result of their various indigenous knowledge about traditional cosmetics. They are mostly applied during traditional rites and festive periods. Occasionally, earthy materials play a vital role in traditionally used cosmetics. Different reasons have been associated with the use of these earthy materials, they are: for skin cleansing, protection against ultra violet radiation, skin lightening, perfecting the distorted part of the skin and improving beauty. This study is focused on the physico-chemical, chemical and mineralogical characterisation of earthy materials indigenously used as cosmetics. This is achieved firstly by identifying the various earthy materials applied topically as well as their constituents. Samples for this study were obtained from six (6) different African countries namely: Botswana, Cameroon, Democratic Republic of the Congo, Nigeria, South Africa and Swaziland and were subjected to the following analyses: Scanning Electron Microscope and Electron Dispersive X-ray Spectroscopy for the morphology and elemental analysis, hydrometer method for the determination of particle sizes of each sample and a texture Auto Lookup Software Package (TAL Version 4.2) for the classification of their various textures (%clay, %sand and %silt). The X-ray diffractometry was applied for the identification of their mineral phases (secondary, major and minor). The Brunauer Emmett and Teller (BET) method was used for the physisorption analysis and classifying them according to their isotherm types (Type I, II, III, IV, V and VI). The chemical analysis was achieved by X-ray fluorescence (XRF). The result revealed that the morphology of the various representative samples varies, except CMR 1; 2, SCC 1; 2 and SLW 1; 2 which showed same structure and same elemental constituents, their resemblance indicated that they possess same geological formation. The XRF result indicated the presence of the following trace elements: Al, As, Au, Ba, Bi, Br, Ca, Cd, Ce, Cl, Co, Cr, Cs, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, I, In, K, La, Lr, Lu, Mg, Mn, Mo, Na, Nd, Ni, Nb, Os, P, Pb, Pd, Pr, Pt, Re, Rh, Ru, S, Sc, Se, Sb, Si, Sm, Sn, Sr, Ta, Te, Tb, Th, Ti, U, V, W, Y, Yb, Zr and Zn, were measured in ppm. For example, Fe – 66.47 (Qwa-Qwa), Al – 4.64 (Swaziland), Si – 6.26 (Democratic Republic of Congo), Ti – 3.75 (Qwa-Qwa) and so on. From the particle size distribution analysis, some samples were identified to be clay (BTS 1, BTS 2, NG 1, SCC 4, SCC 5, SCC 9, SCC 11, SCC 12, SWL 1 and SWL 2) with their particle sizes < 2μm, whereas other samples showed other properties which are > 2 μm. Ten minerals were identified in the clay fraction samples: albite, goethite, halloysite, hematite, kaolinite (kaolinite-1Md, kaolinite 1) Mica (muscovite), sulphur, talc, chalcanthite and whewellite. The BET method vii for physical adsorption revealed that BTS 1, BTS 2, CMR 1, CMR 2, DRC A, DRC B, NG 1, NG 2, SWL 1, SWL 2, SCC 1, SCC 4, SCC 5, SCC 8, SCC 9, SCC 11 and SCC 12 countries possess Type II isotherm whereas samples from SCC 2, SCC 6, SCC 7 and SCC 10 had Type III isotherm. The physisorption analysis result also determined the various surface areas and porosity of each representative samples.