Preparation and Identification of Heavy Minerals for Archaeometrical Studies: Villa of Fiumana (FC), Italy

A new protocol for the laboratory preparation of archaeological samples, aimed at concentrating and analysing heavy minerals by optical microscope and Raman spectroscopy, is presented. The potential of heavy-mineral studies in geoarchaeology could be enhanced conspicuously by using a state-of-the-art protocol for sample preparation, analysing potteries, tempers and archaeological items, by high-resolution mineralogical analyses in medium silt and fine sand (15–250 μm). This method is repeatable by different operators, achievable in reasonable times, applicable also with a few grams of materials, and it is conceived to remove the abundant clayey and fine and very fine silt and liberate minerals from the ground mass. To test the proposed protocol, the mineralogical composition of 5 samples (common wares, red-painted ceramics and amphorae), collected in a Roman Villa sited in Fiumana, Forlì-Cesena, Italy, was investigated. The grain size analysed is representative (63%–75% in weight), and the amount of the ‘heavy fraction’ is very low (0.35%–0.72%), but sufficient to prepare a grain mount. Metamorphic versus magmatic minerals were quantified using a transmitted light, polarizing microscope, coupled with a Raman spectrometer and the presence of opaque and semi-opaque grains using an oblique light. This quantitative study allows us to differentiate samples that have been hand-crafted using different sediments as raw materials, discussing the source from the Alps and collected from the modern Po River depositional area; the sedimentary rocks of the Apennines; the volcanic source rocks from the Roman Province. This protocol is conceived to help improve the quality of heavy-mineral separation for applications in geoarchaeology.