Mineralogy and chemistry of archaeological ceramic fragments from archaeological Dark Earth site in Colombian Amazon

Abstract

Several Archaeological Dark Earth (ADE) sites have been already found in the Colombian Amazon forest showing high content of archaeological ceramic fragments similarly to those in the Brazilian Amazon represented by Quebrada Tacana site. Their fragments are yellow to grey colour, display a burned clayey matrix which involves fragments of cariapé and coal and ash particles, besides grains of quartz and micas. The clay matrix is made of metakaolinite, quartz, and some mica flakes, chlorite and sepiolite. Cariapé and cauixi spicules are constituted of cristobalite, which is also the main mineral component of the coal and ashes. Although not detected by X-ray diffraction, the phosphate minerals should be present, since the contents of phosphor reach up to 2.90 Wt.% P2O5. Possibly it occurs as aluminium-phosphate, since Ca contents fall below 0.1 Wt.%. These mineralogical and chemical characteristics allow to correlate these ceramic fragments with those found in the ADE in Brazil and reinforce phosphor as an important chemical component, which indicates human activity by the daily use of pottery all over the Amazon region.