Mineralogical and chemical characterization of ochres used by the Himba and Nama people of Namibia

Abstract

Ochre is a natural iron oxide earth pigment that can vary from light yellow to intense oranges and to deep reds. Ochre-derived pigments were and continue to be widely used as face and body decoration, sun protection, mosquito repellant, geophagicearths and coloring agents. The Himba and Nama people of Namibia are among modern ethnic groups that still extensively use red and yellow ochre. Eight red ochre samples from Ruacana, northern Namibia and one red and one yellow ochre samples from Keetmanshoop area, southern Namibia used by the Himba and Nama people, respectively were studied by stereomicroscopy, X-ray diffraction (XRD) for mineralogical identification, qualitative scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), inductively coupled plasma mass spectrometry (ICP-MS) for major and trace element abundances. All nine red ochre samples contain hematite, the mineral responsible for the red color of the ochres. Quartz and biotite are also found in nearly all samples. Carbonates, magnetite, apatite, corundum, goethite, feldspar, and kaolinite are found as accessory phases. No hematite was detected in the Nama yellow ochre sample, which contains only goethite. The use of ochre as a geophagic substance by indigenous people of the world is common and consumption of ochre is the most likely route of potential exposure to toxic heavy metals that are found as trace elements in the ochre for the Himba and Nama people. Major and trace element abundances of these ochre samples were determined by ICP-mass spectrometry. The concentrations of the toxic metals (Ac, Cr, Pb) are found to be below permissible levels, thus they do not pose an excessive health risk if applied to human skin or if ingested.