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Stone Beads from Late Bronze Age and Early Iron Age Settlements from South-Western Portugal: Analyses by X-Ray Diffraction.

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Stone Beads from Late Bronze Age and Early Iron Age Settlements from South-Western Portugal: Analyses by X-Ray Diffraction.
  Stone Beads from Late Bronze Age and EarlyIron Age Settlements from South-WesternPortugal: Analyses by X-Ray Diffraction A.P. Gonc¸alves, A.M. Monge Soares, A.C. Silva, and L. Berrocal-Rangel 1 Introduction The use of non-destructive techniques is very important in the field of archaeology,as frequently the specimens are unique and often small, and damaging them may bevery problematic. X-ray diffraction can be used in a non-destructive way, andprovides important information not only on the crystal structure but also on thecomposition of the specimens. It can be used in the characterisation of small and bigspecimens, and it is also possible to scan their surfaces in order to detect andidentify inhomogeneities.In the present study, a set of 19 stone beads (Fig. 1) discovered during archaeo-logical excavations or surveys at three proto-historic settlements from south-westPortugal, namely Castro dos Ratinhos, A´lamo and Salsa 3, were analysed using X-raydiffraction in order to identify the rocks or minerals used for their manufacture.Castro dos Ratinhos is a fortified settlement with Late Bronze Age and EarlyIron Age occupations (Silva and Berrocal-Rangel 2005; Berrocal-Rangel and Silva2007). Fourteen stone beads ascribed to these two occupations and a small blackglass bead, this one pointing out to an Oriental connexion, were retrieved duringarchaeological excavations that took place during the last 4 years. Salsa 3 was theobject of archaeological investigations during 2006 and 2007; Late Bronze Age andEarly Iron Age occupations were also identified at this archaeological site. Twobeads were selected from this site. A´lamo is a fortified settlement, apparently withonly one occupation, of Late Bronze Age chronology. The three beads analysed wererecovered during an archaeological survey. All these proto-historic settlements are A.P. Gonc¸alves ( * ) and A.M.M. SoaresInstituto Tecnolo´gico e Nuclear, Estrada Nacional 10, 2686-953 Sacave´m, Portugale-mail: apg@itn.ptA.C. SilvaDirecc¸a˜o Regional de Cultura do Alentejo, R. de Burgos, 5, 7000-863 E´vora, PortugalL. Berrocal-RangelUniversidad Auto´noma de Madrid, Ciudad Universita´ria de Cantoblanco, 28049 Madrid, SpainI. Turbanti-Memmi (ed.),  Proceedings of the 37  th  International Symposium on Archaeometry ,DOI 10.1007/978-3-642-14678-7_32, # Springer-Verlag Berlin Heidelberg 2011227  located in the Guadiana Valley, close to the Portuguese–Spanish border, withdistances between them smaller than 40 km (Fig. 1).To the best of our knowledge, this work represents the first study of a set of proto-historic stone beads from Portuguese archaeological sites. Green stone beads fromthe Neolithic and Chalcolithic periods have been previously subject to analyses usingpowder X-Ray diffraction, which, due to the destructive nature of the method, wereonly carried out on broken beads (Caneˆlhas 1973; Gonc¸alves 1979). More recently, a bead from a burial necklace with 17 stone beads found in a cist of the south-westernMiddle Bronze Age necropolis of Carapinhais (see Fig. 1) was analysed by SEM,revealing a mineral belonging to the chlorite group (Gonc¸alves 2007). Using thesame technique that we use in our study, supplemented by an Energy DispersiveX-ray Fluorescence (EDXRF) analysis, a bead of talc from a south-western BronzeAge burial was also previously analysed (Gonc¸alves et al. 2005). 2 Experimental X-ray diffraction was used to identify the rocks and/or minerals that constitute thestone beads. A particular sample holder was developed in order to hold and placethe entire collection of stone beads in the proper positions required to perform the Fig. 1  Stone beads and location of the archaeological sites where the beads were discovered228 A.P. Gonc¸alves et al.  X-ray diffraction experiments. The X-ray diffraction system consisted of an X’PertPanalytical diffractometer with a Bragg-Brentano assembly. The scans were per-formed at room temperature, in a reflection mode, using monochromatic CuK a radiation (1.54056 A˚) and under set conditions of 45 kV and 40 mA. The data weremeasured with a 2 y  step size of 0.02  in a 2 y -range of 5   –65  and a counting time of 3 s per step, in order to obtain good statistical data. Phase identification was derivedfrom the X-ray diffraction data using the PowderCell programme (Nolze andKrauss 2000). 3 Results and Discussion A first observation of the X-ray diffraction data of all samples immediately showsthat mostof the stone beads are composed of the same rock or mineral (Fig.2). Onlyone bead, sample A, collected at Castro dos Ratinhos, shows a significantlydifferent X-ray diffraction spectrum, pointing to a dissimilar composition. This isin agreement with the macroscopic observation of the stone beads, where onlysample A appeared different and was made of a soft green stone, in contrast with theother beads, which were made of hard brown-red stones.The spectra obtained for the majority of the samples have the most intense peakat 2 y  ~26.65  ,followed by intense peaks at ~20.87  , ~39.44  , ~50.14  , and ~59.97  .This clearly indicates that the material used for all of the stone beads, with theexception of sample A, is quartz. The quartz used in the manufacture of these beadsis of the carnelian variety. This aspect is also rendered in some identical elementaland X-ray diffraction patterns, pointing out to a similar mineralogical compositionand suggesting the same lithological srcin for the carnelian beads. 204060 A R a t i n h o s S a l s a  3  2  θ    (  °  )   Á l  a m o  Fig. 2  X-ray diffractionpatterns of the stone beadsStone Beads from Late Bronze Age and Early Iron Age Settlements 229  The diffractogram obtained for sample A has a much larger number of peaks, themost intense ones being at 2 y  ~12.47  , ~18.76  , ~19.70  , ~20.98  , ~23.08  , ~25.10  ,~35.43  , ~36.95  , ~45.37  , ~60.18  , and ~67.19  . This indicates that: (1) either theconstituent stone is composed of several different minerals or (2) it is composed of a mineral with low structural symmetry. The analysis of the position and intensityof the peaks allowed us to conclude that stone bead A is mainly composed of onlyone mineral, belonging to the chlorite group, most probably clinochlore.The clinochlore constitution of sample A has parallels with the aforementionednecklace with 17 similar beads found in the SW Bronze Age necropolis of Car-apinhais, not far (approximately 30 km) from Castro dos Ratinhos (Fig. 1).The uniformity of the material used for the manufacture of the beads found inCastro dos Ratinhos, A´lamo and Salsa 3 contrasts with the general variety of stonesused in earlier times (in Neolithic or Chalcolithic times, for instance) for producingthis type of artefacts. Beads in carnelian seem to be common in SW Iberian proto-historic settlements (Gibson et al. 1998). However, due to the lack of geologicalstudies concerning this type of rock, it is not possible to identify the lithologicalsrcin of the carnelian beads found in the south-west of the Iberian Peninsula. 4 Conclusion In conclusion, the analysis of the samples by X-ray diffraction, a non-destructivetechnique, allowed us to identify the raw material of all the beads as quartz, with theexception of one (Sample A) made of a soft dark green stone, belonging to thechlorite group, most probably clinochlore, with parallels in a necklace with stonebeads found in the SW Bronze Age necropolis of Carapinhais, not far from Castrodos Ratinhos. Moreover, the quartz used in the manufacture of most of the beads isof the carnelian variety. Identical elemental and X-ray diffraction patterns pointtoward a similar mineralogical composition, suggesting the same lithological srcinfor the carnelian beads, an srcin which, however, was impossible to determine.This uniformity of the material used for the manufacture of the beads contrasts withthe variety of stones used in earlier times (Neolithic or Chalcolithic) in the makingof this type of artefacts. References Berrocal-Rangel L, Silva ACS (2007) O Castro dos Ratinhos (Moura-Alqueva, Portugal): Umcomplexo defensivo no Bronze Final do Sudoeste peninsular. In: Moret P, Berrocal-Rangel L(eds) Paisajes Fortificados de la Edad del Hierro. Las Murallas Prohistoricas de la Meseta yde la Vertiente Atla´ntica en su contexto europeo. Real Academia de la Historia/Casa deVelazquez, Madrid, pp 169–190Caneˆlhas MGS (1973) Estudo radiogra´fico de “calaı´tes” portuguesas. Revista de Guimara˜es83(1/4):125–145230 A.P. Gonc¸alves et al.  GibsonC,CorreiaVH,BurgessCB,BoardmannS(1998)AltodoCastelinhodaSerra(Montemor-o-Novo, E´vora, Portugal). A Preliminary Report on the excavations at the Late Bronze Age toMedieval Site, 1990–1993. J Iberian Archaeol 0:189–244Gonc¸alves AAHB (1979) Elementos de adorno de cor verde provenientes de estac¸o˜es arqueolo´-gicas portuguesas. Importaˆncia do seu estudo mineralo´gico. In: Actas da 1 a Mesa-Redondasobre o Neolı´tico e o Calcolı´tico em Portugal (Porto, Abril de 1978), pp 209–225Gonc¸alves AAHB (2007) Identificac¸a˜o mineralo´gica de uma conta da Necro´pole dos Carapinhais(Sobral da Adic¸a, Moura). Vipasca. 2 a Se´rie, vol 2. pp 191–193Gonc¸alves AP, Vale´rio P, Soares AMM, Arau´ jo MF (2005) A stone bead from a SW Bronze Ageburial: analysis by EDXRF and X-ray diffraction, O Arqueo´logo Portugueˆs, Se´rie IV, vol 23.pp 257–264Nolze G, Krauss W (2000) PowderCell 2.3 Program. BAM, BerlinSilva AC, Berrocal-Rangel L (2005) O Castro dos Ratinhos (Moura), povoado do Bronze Final doGuadiana: 1 a campanha de escavac¸o˜es (2004). Revista Portuguesa de Arqueologia 8(2):129–176Stone Beads from Late Bronze Age and Early Iron Age Settlements 231
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