A variscite é um mineral raro que oferece uma excelente opotunidade de estudo dos padrões de comércio e troca na Europa durante a Pré-
História através da determinação da sua fonte de proveniência.
No presente texto será discutida a proveniência das contas de colar verdes com base em análises de XRF e XRD, através das quais se criou
uma identidade geoquímica passível de ser comparada com as das fontes de variscite conhecidasVariscite is a rare mineral that offers an excellent opportunity to study trade and exchange patterns in prehistoric Europe through proveniencing of
source material.
In this paper we discuss the provenance of Perdigões’ green beads by means of XRF and XRD analyses, thus creating a geochemical baseline that
is compared with that of the known variscite source

Hurtado Pérez, Víctor

Linares Catela, José Antonio

Odriozola Lloret, Carlos Patricio

English

idUS. Depósito de Investigación Universidad de Sevilla

Apontamentos de Arqueologia e Património –  6 / 2010  (www.nia-era.org)  - 47 -                   1. Introdution A major research question in the study of prehistoric Iberia is the analysis of traded objects and their implications for understanding social interaction, in a period, 3rd millennium BCE, known by its importance in the discussion of a set of social changes of structural relevance -i.e. the appearance of permanent hierarchies, class societies or the state, the development of the social inequality and more institutionalised forms of power, … Exchange and mobility patterns are, thus, of outmost importance in the understanding of prehistoric Iberia.  The study of the green beads from tholos 1 and 2 from Perdigões will help to understand the Rivera do Alamo complex net of interactions in which Perdigões would have act as a central place of an aggregated network, as claimed by Valera (2006) and further evidenced by pottery studies performed by Dias et al. (2008).         Carlos P. Odriozola1, J. A. Linares-Catela2  e V. Hurtado-Pérez1               The idea under our study is to understand the details of Prehistoric exchange patterns, towards what exchange theories developed since the mid 1970’s (i.e., Earle and Ericson, 1977, Weigand et al., 1977) have been highly successful, specifically in terms of scarce resources such as rare minerals and ores. The more rare the resource, the more successfully its source can be tracked simply due to the fewer number of potential sources available. Rare minerals and ores, then, offer an excellent opportunity to study trade and exchange patterns in prehistoric Europe through provenance of source material.          Resumo:  Análise de proveniência das contas verdes dos Perdigões A variscite é um mineral raro que oferece uma excelente opotunidade de estudo dos padrões de comércio e troca na Europa durante a Pré-História através da determinação da sua fonte de proveniência. No presente texto será discutida a proveniência das contas de colar verdes com base em análises de XRF e XRD, através das quais se criou uma identidade geoquímica passível de ser comparada com as das fontes de variscite conhecidas.  Abstract: Variscite is a rare mineral that offers an excellent opportunity to study trade and exchange patterns in prehistoric Europe through proveniencing of source material. In this paper we discuss the provenance of Perdigões’ green beads by means of XRF and XRD analyses, thus creating a geochemical baseline that is compared with that of the known variscite sources.   1 Instituto de Ciencia de Materiales de Sevilla, CSIC. 2 Cota Cero GPH S.L.  3 Dpto. de Prehistoria y Arqueología, Universidad de Sevilla. PERDIGÕES’ GREEN BEADS PROVENANCE ANALYSIS Figure 1 – Location of the Iberian variscite sources and location of Perdigões. Apontamentos de Arqueologia e Património –  6 / 2010  (www.nia-era.org)  - 48 -  Variscite is, thus, a wonderful resource for provenance study as it is a scarce naturally occurring hydrated aluminium phosphate. In the Iberian Peninsula, only five main sources occur (figure1): Can Tintorer (Gavá, Barcelona), Palazuelos/El Bostal (Aliste, Zamora), Punta Corbeiro (Sanxenxo, Pontevedra), Pico Centeno (Encinasola, Huelva) in Spain and Bragança (Tras-o-Montes) in Portugal. Thus, a high degree of precision and accuracy can be achieved due to the limited number of available geological outcrops in which the mineral is found. 2. Materials and methods In this paper we performed a provenance analysis of 20 green beads (figigure 2) from Perdigões’ (Reguengos de Monsaraz, Portugal) tholoi 1 and 2 (Valera et al., 2002). X-ray fluorescence and diffraction analyses of the beads provided a baseline mineral signature that if compared to sources outlines the origin of the raw material used for bead working. Non-destructive compositional data were obtained using a µ-XRF, while non-destructive XRD patterns were recorded with a parallel beam using a Goebbels mirror set. Beads were analysed with an Eagle III EDAX µ-XRF and by means of X-ray Difraction with a Siemens D5000 difractometer. X-ray diffraction patterns were obtained using a Siemens D5000 θ/2θ diffractometer with Cu Kα source operating at 50 kV, 35 mA. A parallel Goebel-mirror beam from a Cu Kα source was used and the data were collected on transmission mode with a 2D detector. Patterns were obtained using a step width of 0.02° 2θ between 3° and 65° 2θ and a counting time of 10 s per step at ambient temperatures.  X-ray fluorescence compositional data was obtained by focusing directly over the sample with an optical microscope; an area of 100 µm was analyzed using a Kα radiation produced by a Rh tube operated at 40 kV. The elemental composition of the samples is expressed as weight percentage of the corresponding oxides. Beads from Perdigões tholoi 1 and 2 were randomly sampled from the more than 3000 turquoise-green beads recovered in each tomb. Due to the variety of bead shapes that occurred in the tholoi, the major sampling criteria was to insure all bead shapes were represented in the sample.  3. Results and discussion Variscite is also known as ‘callaite’. This term was first used by Pliny (Natural History XXXVIII) to describe all green rocks with a shiny luster, which then also became attached to variscite. Since the mid 1970s the term ‘callaite’ has been strongly criticized in its general use when alluding to variscite beads (Dominguez Bella, 2004), although only recent studies (Edo et al., 1995, Pozo et al., 2002, Villalba, 2002, Querré et al., 2007, 2008) have proven that not all green or green-bluish shiny lustrous rocks used in bead production were made of variscite. In fact, the raw material for bead              production was much more varied than expected, and strengite, muscovite, chlorite, sericite and talc have all been noted as raw materials. The mineralogical characterization of Perdigões’ beads revealed that the great majority of green beads from tholoi 1 and 2 match the variscite ICDD 25-18 card (fig. 3); and that only 3 beads do not match variscite pattern which appear to match muscovite XRD pattern (ICDD 6-263) –table 1.                 Figure 2 – Bead from Perdigões tholos 1. Table 1 – Mineral phase identification for the studied beads. Apontamentos de Arqueologia e Património –  6 / 2010  (www.nia-era.org)  - 49 -             XRD card 25-18 from a Palazuelos variscite sample matches all of the peaks appearing in our variscite samples, while card 33-33 from Utah presents a peak shift to higher 2θ degrees. This might be due to the higher purity of the mineral phase of Utah variscite and to the presence of Fe, Cr, Ni, … substitutions as well as for the intergrowth with metavariscite and quartz as reported for Palazuelos and Pico Centeno sources (Arribas et al., 1971, Salvador and Fayos, 1972, Moro Benito et al., 1992, 1995). XRD patterns, thus, indicate that all variscite beads are orthorhombic cryptocrystalline type M variscite (ICDD 25-18). Once secure that we are dealing with variscite beads, we can return to see whether there are groups of beads that show similar chemical composition and whether they can be associated with a specific source. The relationship between beads and source is established by comparison of the chemical components of the beads and those of the sources. The validity of this approach rests in the fact that ‘[…] differences in chemical composition between different natural sources exceed, in some way, the differences observed within a given source’ (Weigand et al., 1977).          The variscite mineral group are orthorhombic phosphates with a general formula [MPO42H2O], where M = Al3+, Fe3+, Cr3+, V3+. Variscite is a secondary mineral formed by direct deposition of phosphatic groundwater descending along open fissures and reacting with aluminium-rich rocks (Larsen, 1942). It occurs as fine-grained masses in nodules, cavity fillings and crusts associated with clay rocks, typically of schist. Variscite’s pure phases are white and transparent, however its colour ranges from yellow to green hues and massive variscite usually have a waxy, lustrous turquoise-green colour. Colour is, however, dependent on the formation process and the presence of chemical compounds other than P and Al are responsible for the colour that variscite nodules exhibit. Recent spectroscopic studies claim that Chromium (Cr3+) and Vanadium (V4+) are the uniquely responsible for the colour of variscite (Calas et al., 2005). Recent studies show considerable analytical variation for source minor and trace elements. In some cases a coefficient of variation (CV) as high as 1.7 for a single element (Odriozola et al., 2010). These CVs prevents us of using minor and trace elements and their correlations as an indicator of provenance due to its high natural variability. Thus, source natural variability becomes an important barrier to variscite provenance analysis and therefore to its reliability in determining prehistoric exchange patterns. Variscite’s ideal formula is [AlPO42H2O] which means a P/Al atomic ratio equal to 1, although aluminium substitutions for other trivalent transition ions (Fe3+, Cr3+, V3+, …) may slightly increase this ratio. This is consistent with most of the reported data, however, in our case this ratio is much higher than 1, around 1.7 (table 2). The presence of hydrogenphosphate species in the variscite mineral would result in P/Al atomic ratios higher than 1 depending on the exact value and the relative proportions of the different hydrogenphosphate species. These findings suggest the P/Al atomic ratio recorded for Pico Centeno massive variscite and Perdigões beads arose during the genesis of the variscite deposits and resulted from the associated pH and nature of the host-rocks, modifying the concentrations of PO43-, H2PO4- and HPO42 (Odriozola et al.,          Figure 3 – XRD patterns of Perdigões beads with indication of peak position for ICDD card 25-18. Table 2 – chemical composition of the variscite beads from Perdigões Apontamentos de Arqueologia e Património –  6 / 2010  (www.nia-era.org)  - 50 -   2010). Thus, the P/Al atomic ratio should be an indication of provenance as it is established during mineral genesis. This issue has not been addressed in any of the other studied sources where this ratio seems to be ≈1. Assuming the above-mentioned hypothesis, if compared, the variscite beads and the variscite sources P/Al atomic ratio should establish Perdigões beads origins. To what the non-parametric density estimation (figure 4) allows the recognition of the origin of Perdigões variscite beads in Pico Centeno source. Figure 4 shows how the overall sample of Perdigões beads fits into natural Pico Centeno clusters, and therefore can be interpreted as a match between Perdigões beads and Pico Centeno source.                   6. References  ARRIBAS, A., GALÁN, E., MARTÍN-POZAS, J. M., NICOLAU, J. & SALVADOR, P. (1971), "Estudio mineralógico de la variscita de Palazuelo de las Cuevas, Zamora (España)", Studia Geologica, II, p.115-132. CALAS, G., GALOISY, L. & KIRATISIN, A. (2005) The origin of the green color of variscite. American Mineralogist, 90, 984-990. DIAS, M. I., VALERA, A. C., LAGO, M. & PRUDÊNCIO, M. I. (2008) "Proveniência e tecnologia de produção de cerâmicas nos Perdigões", Vipasca, Arqueología e Historia, 2. DOMINGUEZ BELLA, S. (2004), "Variscite, a prestge mineral in the Neolithic-Aneolithic Europe. Raw material sources and possible distribution routes", Slovak Geological Magazine, 10, p.147-152. EARLE, T. K. & ERICSON, J. E. (Eds.) (1977), "Exhange system in Prehistory, New York, Academic Press. 4. Conclusion Based on beads P/Al ratios recorded in the data set and the match with Pico Centeno’s ratio, we claim that the raw material procurement for bead working at Perdigões was Pico Centeno. 5. Acknowledgements The authors acknowledge the Junta de Andalucía, Consejería de Innovación, Ciencia y Tecnología for the financial support (P06-HUM-02159). C.P. Odriozola acknowledges a PhD grant from I3P fellowship program. We must thank the permission to study beads from Perdigões to ERA-Arqueologia S.L. and especially to A.C. Valera.                  EDO, M., BLASCO, A., VILLALBA, M. J., GIMENO, D., FERNÁNDEZ TURIEL, J. L. & PLANA, F. (1995), "La caracterización de la variscita del complejo minero de Can Tintorer, una experiencia aplicada al conocimiento del sistema de bienes de prestigio durante el neolítico", (BERNABEU, J., OROZCO KÖHLER, T. & TERRADAS, X. Eds.), Los recursos abióticos en la Prehistoria. Caracterización, aprovisionamiento e intercambio, Universitat de Valencia. LARSEN, E. S. (1942), "The mineralogy and paragenesis of the variscite nodules from Near Fairfield, Utah part 1", American Mineralogist, 27, p.281-300. ARRIBAS, A., GALÁN, E., MARTÍN-POZAS, J. M., NICOLAU, J. & SALVADOR, P. (1971), "Estudio mineralógico de la variscita de Palazuelo de las Cuevas, Zamora (España)", Studia Geologica, II, p.115-132. Figure 4 – P vs. Al plot with non-parametric density estimation. Apontamentos de Arqueologia e Património –  6 / 2010  (www.nia-era.org)  - 51 -  CALAS, G., GALOISY, L. & KIRATISIN, A. (2005) The origin of the green color of variscite. American Mineralogist, 90, 984-990. DIAS, M. I., VALERA, A. C., LAGO, M. & PRUDÊNCIO, M. I. (2008) "Proveniência e tecnologia de produção de cerâmicas nos Perdigões", Vipasca, Arqueología e Historia, 2. DOMINGUEZ BELLA, S. (2004), "Variscite, a prestge mineral in the Neolithic-Aneolithic Europe. Raw material sources and possible distribution routes", Slovak Geological Magazine, 10, p.147-152. EARLE, T. K. & ERICSON, J. E. (Eds.) (1977), "Exhange system in Prehistory, New York, Academic Press. EDO, M., BLASCO, A., VILLALBA, M. J., GIMENO, D., FERNÁNDEZ TURIEL, J. L. & PLANA, F. (1995), "La caracterización de la variscita del complejo minero de Can Tintorer, una experiencia aplicada al conocimiento del sistema de bienes de prestigio durante el neolítico", BERNABEU, J., OROZCO KÖHLER, T. & TERRADAS, X. Eds.), Los recursos abióticos en la Prehistoria. Caracterización, aprovisionamiento e intercambio, Universitat de Valencia. LARSEN, E. S. (1942), "The mineralogy and paragenesis of the variscite nodules from Near Fairfield, Utah part 1", American Mineralogist, 27, p.281-300. MORO BENITO, M. C., GIL-AGERO, M., CEMBRANOS PÉREZ, M. L., PÉREZ DEL VILLAR, L. & FERNÁNDEZ FERNÁNDEZ, A. (1995), "Las mineralizaciones estratiformes de variscita (Aluminofosfatitas) silúricas de los Sinformes de Alcañices (Zamora) y Terena (Huelva)(España)", Boletín Geológico y Minero, 106, p.233-249. MORO BENITO, M. C., GIL-AGERO, M., MONTERO, J. M., CEMBRANOS PÉREZ, M. L., FERNÁNDEZ FERNÁNDEZ, A. & HERNÁNDEZ SANCHEZ, E. (1992), "Características de las mineralizaciones de variscita asociadas a los materiales silúricos del Sinforme de Terena, Encinasola (Provincia de Huelva). Comparación con las de la provincia de Zamora", Boletín de la Sociedad Española de Mineralogía, 15, p.79-89. ODRIOZOLA, C. P., LINARES CATELA, J. A. & HURTADO, V. (2010), "Variscite Source and Source Analysis: Testing Assumptions at Pico Centeno (Encinasola, Spain)", Journal of Archaeological Science. POZO, CASAS, J. & MEDINA, J. A. (2002), "Estudio mineralógico de componentes ornamentales pétreos procedentes de un yacimiento de la Cultura del Argar (Fuente Álamo, Almería)", Boletín Geológico y Minero, 113, p.131-142. QUERRÉ, G., HERBAULT, F. & CALLIGARO, T. (2007), "Long distance transport of Neolithic variscite ornaments along the European Atlantic arc demonstrated by PIXE analysis", Proceedings of the XI International Conference on PIXE and its Analytical Applications Puebla, Mexico, May 25-29, 2007, UNAM. QUERRÉ, G., HERBAULT, F. & CALLIGARO, T. (2008), "Transport of Neolithic variscites demonstrated by PIXE analysis", X-Ray Spectrometry, 37, p.116-120. SALVADOR, P. & FAYOS, J. (1972), "Some aspects of the structural relationship between "meshbach-Type" and Lucin-Type" variscites", American Mineralogist, 57, p.36-44. VALERA, A. C. (2006), "A margem esquerda do Guadiana (região de Mourão), dos finais do 4.º aos inícios do 2.º milénio AC", ERA-Arqueologia, 7, p.136-210. VALERA, A. C., LAGO, M. & SHAW EVANGELISTA, L. (2002), "Ambientes funerários no complexo arqueológico dos Perdigões: uma análise preliminar do contexto das prácticas funerarias Calcolíticas no Alentejo", ERA-Arqueologia, 4. VILLALBA, M. J. (2002), "Le gîte de variscite de Can Tintorer: production, transformation et circulation du minéral vert", (GUILAINE, J. Ed.) Matériaux, productions, circulations du Neolithique à l'Age du Bronze. Séminaire du Collège du France Paris, Errance. WEIGAND, P. C., HARBOTTLE, G. & SAYRE, E. V. (1977), "Turquoise source and source analysis: Mesoamerica and the Southwestern U.S.A.", Exchange Systems in Prehistory, New York, Academic Press.                                 

Análise de proveniência das contas verdes dos Perdigões

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Análise de proveniência das contas verdes dos Perdigões

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