Mineralogical and geochemical characterization of the concotto artefacts from firing places of Longola protohistoric settlement (Naples)

A set of concotto samples, a type of fired mixture of various raw materials, coming from firing place of the perifiuvial protohistoric site of Longola (Campania region, southern Italy) was characterized by means of a multi-analytical approach, i.e. polarized light optical microscopy (OM), X-ray powder diffraction (XRD), scanning electron microscopy and energy dispersive spectrometry (SEM-EDS), X-ray fluorescence (XRF), inductively-coupled plasma-mass spectrometry (ICP-MS) and Mossbauer spectroscopy. The specimens generally show a heterogeneous texture, a red-coloured groundmass composed of a mixture of tiny quartz, feldspar, poorly-crystallized goethite, hematite and clay minerals. The crystal fractions show significant amounts of quartz and alkali feldspar and variable percentages of clinopyroxene, leucite, biotite, hematite, magnetite and traces of muscovite. Random secondary phases of calcite, vivianite and gypsum have been identified. The coarser fraction is formed by several types of inclusions, i.e. tephra fragments (pumices, scoriae), volcanic and sedimentary rocks. Illite and very subordinate smectite (montmorillonite) were detected by X-ray diffraction. Trace elements also show a contribution of volcanic raw materials. The Mossbauer analyses at 296 K show the occurrence of paramagnetic Fe(3+) iron (clay minerals) and magnetic Fe(3+) iron (hematite). For the 80 K spectrum, however, two doublets (ferrous and ferric iron in clay minerals) and one sextet (hematite). The concotto samples do not suffer high temperatures, perhaps much lower than 500-600 degrees C in a mainly oxidizing atmosphere. Only sporadically, if any, higher temperatures (> 800 degrees C) might have been reached. (Less)