Towards a library of raw ferruginous and manganous rocks: challenges to source coloring rocks used during the Prehistory

Description

From 300 ky, prehistoric people have used pigmentaceous rocks. If the activities relatedto the so called "pigment" uses are difficult to describe, it is principally due to the mode ofutilization. In fact, these mineral resources were mainly ground to powder, which irreme-diably destroyed the structure of the initial rock, and blur the informations concerning theselection of the raw coloring materials, the techniques of transformation implemented and,at least, the utilizations.In order to overcome this critical situation, we focus on the supply. This initial step ofanalysis will benefit to a better understanding of: - the past mineral landscape and the economical areas in which diverse prehistoric peoplesettled transported goods and changed through times,- the choice of raw coloring materials compared to, in one hand, the other geologicalcoloring materials that were available, and, in the other hand, the other resources collected,such as flakable rocks ( Reseau des Lithotheques).- the main sensitive criteria of these choices, i.e. visual and mechanical criteria, whichhave connections with technical preoccupations during the transformation process of the rawrocks by grinding, heating and mixing, and finally may elucidate the utilizations.In this view, we are currently building a library of natural coloring materials. The mainissue is to establish a relevant ID card for each geological deposit taking into account the geological dynamics. As for flakable resources and based on existing methodology, we conduct systematic surveys and documentations of the iron and manganese oxide (hydroxide)containing deposits. We collect information at different scales: petrography, mineralogy and geochemisty in order to find the geologicalfingerprints which could be used to differentiate the geomaterials and to compare with diverse archaeological remains coming from thePaleolithic sites, including coloring fragments, residues on tools and paintings/drawings.The first step of this library called "pigmentotheque" has been initiated between the Ardecheand Gard valleys (south-east of France), considering the high potential of ferruginous depositsin various contrasted geological environments and the closeness with numerous prehistoricsettlements and Paleolithic rock art sites. Comparison and discussion could be done firstlywith the collection of colored and coloring matter artefacts from the " Grotte aux points "and from the " Abri des Pˆecheurs " (Ard`eche), currently studied

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International audience

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