Archaeometric characterization of prehistoric rock paintings, natural mineral pigments and saline efflorescences from archaeological sites

Cavalcante, Luis Carlos Duarte

doi:10.1590/S1981-81222014000100018

THESIS AND DISSERTATIONS

Doctoral Thesis - Post-Graduate Program in Chemistry - Federal University of Minas Gerais - Belo Horizonte (Minas Gerais) - Brazil 2012. cavalcanteufpi@yahoo.com.br

The present experimental work was devoted to the chemical and mineralogical characterization of prehistoric rock paintings, of mineral pigments and of saline efflorescences from archaeological sites located in the states of Piauí, Bahia and Ceará, in Brazil, and in the Perito Moreno National Park, in Argentina. Samples were investigated in the laboratory by several analytical techniques, including (i) ⁵⁷Fe transmission and conversion electron Mössbauer spectroscopy; (ii) grazing incidence X-ray diffraction; (iii) energy dispersive spectroscopy; (iv) scanning electronic microscopy; (v) powder X-ray diffraction; (vi) energy dispersive X-ray fluorescence and (vii) Fourier-transform infrared spectroscopy. Results revelated that the red paintings were basically prepared with hematite (αFe₂O₃)-rich materials; the yellow paintings contained goethite (αFeOOH); the black paintings were essentially composed by carbon, presumably from charcoal (except the sample PCI-03, which was found to contain carbon together with hematite), and the gray painting was prepared with a mixture of carbon and aluminosilicate minerals. The iron oxides and oxyhydroxides appear as being of small particle sizes, high isomorphic substituition of different cations for iron and low crystallinity. Results related to saline efflorescence samples revealed the occurrence of chabazite (Ca₂Al₄Si₈O₂₄.12H₂O); partheite (Ca₂Al₄Si₄O₁₅(OH)₂.4H₂O); taranakite (H₆K₃Al₅(PO₄)₈.18H₂O); newberyite (MgHPO₄.3H₂O); kaolinite (Al₂Si₂O₅(OH)₄); brushite (CaPO₃(OH).2H₂O); gypsum (CaSO₄.2H₂O); KAl₃(SO₄)₂(OH)₆; potassium aluminum sulfate (KAl(SO₄)₂); K₂SO₄.7KHSO₄.H₂O and 5ZnO.Al₂O₃.ZnSO₄.15H₂O. The red pigments contained predominantly hematite, together with quartz, kaolinite, illite and KAl₃(SO₄)₂(OH)₆, whereas the yellow pigment contained goethite, quartz and kaolinite. The white pigment was composed mainly by illite and quartz.