The ceramic artifacts in archaeological black earth (terra preta) from lower Amazon region, Brazil: mineralogy

Abstract

Several archaeological black earth (ABE) sites occur in the Amazon region. They contain fragments of ceramic artifacts, which are very important for the archaeological purpose. In order to improve the archaeological study in the region we carried out a detailed mineralogical and chemical study of the fragments of ceramic artifacts found in the two ABE sites of CachoeiraPorteira, in the Lower Amazon Region. Their ceramics comprise the following tempers: cauixi, cariapé, sand, sand +feldspars, crushed ceramic and so on and are composed of quartz, clay equivalent material (mainly burned kaolinite), feldspars, hematite, goethite, maghemite, phosphates, anatase, and minerals of Mn and Ba. Cauixi and cariapé, siliceous organic compounds, were found too. The mineralogical composition and the morphology of their grains indicate a saprolite (clayey material rich on quartz) derived from fine-grained felsic igneous rocks or sedimentary rocks as source material for ceramic artifacts, where silica-rich components such cauixi, cariapé and/or sand (feldspar and rock fragments) were intentionally added to them. The high content of (Al,Fe)-phosphates, amorphous to low crystalline, must be product of the contact between the clayey matrix of pottery wall and the hot aqueous solution formed during the daily cooking of animal foods (main source of phosphor). The phosphate crystallization took place during the discharge of the potteries put together with waste of organic material from animal and vegetal origin, and leaving to the formation of the ABE-soil profile. KEY WORDSTerra Preta, Black Earth, Archaeological ceramic fragment, Lower Amazon, Phosphates, Mineralogy.Artefatos cerâmicos em sítios arqueológios com terra preta na região do baixo Amazonas, Brasil: Mineralogia. RESUMO Sítios arqueológicos com Terra Preta, denominados de Terra Preta de Índio ou ainda Terra Preta

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

“…In the ADE site at Bragança, located at north eastern of state Para, well formed crandallite crystals have been identified (Costa et al, 2006). Variscite and variscite-strengite have been identified at Cachoeira-Porteira, in the Lower Amazon region (Costa et al, 2004a). The phosphor contents of Quebrada Tacana cannot be related either to apatite, rarely found as bone fragments inside of the fragments, for example at Cachoeira-Porteira (Costa et al, 2004a), nor to crandallite or crandallite-goyazite, since the contents of CaO (Table 1) and SrO (not indicated at Table 1) are very low (< 0.10 Wt.%).…”

“…Variscite and variscite-strengite have been identified at Cachoeira-Porteira, in the Lower Amazon region (Costa et al, 2004a). The phosphor contents of Quebrada Tacana cannot be related either to apatite, rarely found as bone fragments inside of the fragments, for example at Cachoeira-Porteira (Costa et al, 2004a), nor to crandallite or crandallite-goyazite, since the contents of CaO (Table 1) and SrO (not indicated at Table 1) are very low (< 0.10 Wt.%). The chemical composition of the ceramic fragments is not homogeneous in terms of phosphor and iron ( Figure 5) and suggests a raw material for pot production based on quartz and kaolinite as the main mineral phases, besides iron oxyhydroxide minerals in variable proportions.…”

“…(Table 1), which could correspond to ca. 1.5 to 8.7 Wt.% of aluminium phosphates, the possible phosphate minerals, found in the ceramic fragments (Costa et al, 2004a(Costa et al, , 2006(Costa et al, , 2009. SEM images and EDS chemical analyses confirm the presence of phosphor in the clayey matrix.…”

“…Phosphor normally occurs as non-crystalline sub-micrometre masses in the burned clayey matrix as well as around the cariapé fragments and cauixi spicules. Chemically, the phosphor presence can be correlated to aluminium (iron) phosphates and occasionally crandallite and variscite (Costa et al, 2004a(Costa et al, , 2006. The occurrence of phosphate in the ceramic materials of ADE can add very important insights about the exposure of the respective pot to phosphor-rich foods or even to some phosphor-bearing natural material used as fluxes which were in fact not known concerning the Amazonian archaeological potteries until the present, since they don't display any king of glass.…”

“…The matrix displays sub-round to angular submillimeter quartz grains, besides cariapé fragments and cauixi spicules already mentioned. The cauixi (Tubella reticulata and Parnula betesil), for example, is fresh water spongy that cumulates on trunks of trees, boats, and so on and cariapé is a tree outer skin representing a Bignomiacea, Moquilea, Licania utilis, and Turiuva (Costa et al, 2004a).…”