Mõssbauer spectroscopy and dating by fission traces in provenience studies of archaeomaterials: obsidian artefacts

A obsidiana foi urna das matérias primas mais utilizadas na industria lírica pré-histórica; é encontrada em numerosos sitios arqueológicos de regiões vulcânicas, e também, em lugares às vezes distantes de sua origem. A busca de fontes naturais de onde provêm as obsidianas, encontradas em sitios arqueológicos, permite uma melhor compreensão dos sistemas de troca e/ou proveniência destes objetos. Por suas características físico-químicas e de afloramento, a obsidiana é urna das rochas preferidas para este tipo de estudo. Neste artigo, descrevemos brevemente dois métodos físicos atualmente utilizados em estudos de proveniência de obsidianas arqueológicas, a espectroscopia Mõssbauer e a datação por traços de fissão, onde são dados alguns exemplos de aplicação e comentadas as perspectivas oferecidas por esses métodosObsidian was one of the most widely used raw materials of the prehistoric lithic industry. It is present in many archaeological sites from volcanic provinces, but also in sites sometimes very far from any volcano. To look for the natural outcrop from where any particular archaeological obsidian was extracted is of prime importance to contribute to the knowledge of past trade networks and/or procurement strategies. Because of its physico-chemical and outcropping characteristics, obsidian is one of the preferred rocks for provenance studies. In this article, we describe briefly two physical methods presently used in obsidian sourcing, Mõssbauer spectroscopy and fission track dating. A few examples and the research perspectives offered by these approaches are commente

Druse clinopyroxene in D'Orbigny angritic meteorite studied by single-crystal X-ray diffraction, electron microprobe analysis and Mössbauer spectroscopy

The crystal structure of druse clinopyroxene from the D’Orbigny angrite, (Ca0.944 Fe2+ 0.042 Mg0.010Mn0.004) (Mg0.469Fe2+ 0.317Fe3+ 0.035Al0.125Cr0.010Ti0.044) (Si1.742Al0.258) O6, a = 9.7684(2), b = 8.9124(2), c = 5.2859(1) Å, β = 105.903(1)°, V = 442.58 Å3, space group C2/c, Z = 2, has been refined to an R1 index of 1.92% using single-crystal X-ray diffraction data. The unit formula, calculated from electron microprobe analysis, and the refined site scattering values were used to assign site populations. The distribution of Fe2+ and Mg over the M1 and M2 sites suggests a closure temperature of 1000 °C. Mössbauer spectroscopy measurements were done at room temperature on a single crystal and a powdered sample. The spectra are adequately fit by a Voigt-based quadrupole-splitting distribution model having two generalized sites, one for Fe2+ with two Gaussian components and one for Fe3+ with one Gaussian component. The two ferrous components are assigned to Fe2+ at the M1 site, and arise from two different next-nearest-neighbor configurations of Ca and Fe cations at the M2 site: (3Ca,0Fe) and (2Ca,1Fe). The Fe3+/Fetot ratio determined by Mössbauer spectroscopy is in agreement with that calculated from the electron microprobe analysis. The results are discussed in connection with the redox and thermal history of D’Orbigny.Fil: Abdu, Yassir A.. University of Manitoba; CanadáFil: Scorzelli, Rosa B.. Centro Brasileiro de Pesquisas Físicas; BrasilFil: Varela, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Kurat, Gero. Naturhistorisches Museum; AustriaFil: Souza Azevedo, Izabel de. Centro Brasileiro de Pesquisas Físicas; BrasilFil: Stewart, Silvana Jacqueline. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Hawthorne, Frank C.. University of Manitoba; Canad

Tendances actuelles dans la caractérisation des obsidiennes pour les études de provenance

Les recherches de provenance des obsidiennes de sites paléolithiques et néolithiques connaissent actuellement une grande expansion, notamment par leur intégration dans les études de chaînes opératoires, qui nécessitent de déterminer l’origine de la matière première de séries importantes de pièces archéologiques. Il existe par ailleurs une forte demande de mesures peu à non destructives et éventuellement à effectuer in situ. D’où un certain nombre de développements méthodologiques récents. Le but de cette contribution est d’en présenter le statut actuel.Sourcing studies involving obsidians from Palaeolithic and Neolithic sites are presently undergoing a period of change, notably in terms of the average number of samples analyzed per project, due largely to their integration into the chaînes opératoires approach of lithic technologies. This can entail working with a large number of artifacts from an archaeological context. There is also an ever-increasing demand to employ quasi non-destructive characterization methods and completely non-destructive methods that eventually could be performed in situ. As such, recent methodological advances have taken several directions. The purpose of this short note is to give an overview of these approaches

Precious metals determination in ancient coins by portable ED-XRF spectroscopy with a 238Pu source

A portable X-ray fluorescence system (pXRF) was employed to analyse a set of gold, silver and billon coins from the collection of the Museu Histórico Nacional do Rio de Janeiro (MHN), struck during the Brasil Colônia period, under the Dutch occupation, and in Portuguese mints under the reigns of Fernando I (1367 to 1383) and his successor João I (1383 to 1433). The experimental setup consisted of a mini Si-PIN detector and a radioactive source of 238Pu for the excitation of the samples. The aim of the study was to test the possibilities and limitations of this portable system for the determination of the coins’ base alloys, and to verify whether the results obtained were consistent with historical facts. The Brasil Colônia period coins show about 80.5% gold and 96.8% silver. For the Portuguese coins, we could identify a possible monetary debasement during the reign of João I. No matrix corrections were made for these preliminary results.Un équipement portable à fluorescence X (pFX) a été utilisé pour l’analyse de monnaies en or, en argent et en billon appartenant à la collection du Museu Histórico Nacional de Rio de Janeiro (MHN). Certaines de ces monnaies ont été frappées au Brésil pendant la période Brasil Colônia et sous l’occupation hollandaise, alors que d’autres ont été frappées au Portugal sous les règnes de Ferdinand I (1367-1383) et de son successeur Jean I (1383-1433). Le montage expérimental est constitué d’un mini détecteur Si-PIN et d’une source radioactive de 238Pu, dont la radiation émise est utilisée comme source d’excitation. Le but de ce travail est double : vérifier les possibilités et les limites de ce système portable lors qu’il s’agit de déterminer les alliages constitutifs de monnaies en métal précieux et vérifier les rapports entre l’évolution des compositions des monnaies et les différents faits historiques. Les monnaies appartenant à la période Brasil Colônia sont constituées de 80,5 % d’or et de 96,8 % d’argent et les monnaies frappées au Portugal montrent une dévaluation sous Jean I

Caracterização Mineralógica de uma Bentonita da Mina Bravo, Boa Vista, Paraíba

A bentonite sample from Bravo mine, Boa Vista District (Paraíba, NE Brazil), presenting the high Cation Exchange Capacity (CEC) of 106meq/100g, was thoroughly characterized, in order to find the best added- value application for it. Smectite, quartz, and jarosite have been identified in the run of mine (ROM) sample, whereas the size fraction under 10μm contains only smectite with traces of quartz. All the iron in the sample is Fe3+, as analysed by 57Fe Mössbauer Spectroscopy, and its sole carriers are smectite, exclusively in the octahedral layer, and goethite, around 30% (wt) in both samples. According to solid state 27Al Nuclear Magnetic Ressonance, only 1% of the aluminium is located in the tetrahedral layer of the smectite, whereas 99% of it is octahedral. The clay’s chemical composition and its spectroscopic signature classify the chocolate bentonite as an iron-rich montmorillonite. Thermal analysis, with an endothermic peak due to smectite dehydroxylation at 488.6°C, and FTIR (Fourier Transformed Infrared) Spectroscopy, confirm the classification.A bentonita chocolate, oriunda da mina Bravo, Boa Vista, PB, foi detalhadamente caracterizada como subsídio a uma aplicação de maior valor agregado, considerando sua elevada capacidade de troca catiônica (CTC) – 106meq/100g. Foram identificados esmectita, quartzo e jarosita na amostra bruta, e a fração fina, abaixo de 10μm, contém apenas esmectita, com traços de quartzo. A espectroscopia Mössbauer do 57Fe indicou que todo o ferro da amostra é trivalente, carreado por goethita (de 28 a 32% do total) ou na camada octaédrica da esmectita. Ressonância Magnética Nuclear de 27Al no estado sólido (RMN-MAS de 27Al) indicou que apenas 1% do Al da amostra situa-se na camada tetraédrica da esmectita, estando o restante na camada octaédrica. A composição química da amostra, associada às considerações espectroscópicas, classificou a esmectita como uma montmorillonita rica em ferro. As análises termodiferenciais/ termogravimétricas, com o pico endotérmico de desidroxilação do argilomineral centrado em 488,6°C, e as análises de espectroscopia na região do infravermelho confirmam a classificação

Meteorites: messengers from the outer space

Tens of millions of meteoroids, solid bodies from the outer space, enter the Earth's atmosphere each year. They are pieces of stone, iron or stony-iron conglomerates, ranging in mass from fractions of a gram to hundreds of kilograms. Those that survive the passage through the atmosphere and fall to Earth are called meteorites. Meteorites are the most ancient and primitive rocks as old as the Solar system. The study of these enigmatic objects intrigued scientists since ancient times, not only about their place of origin but also about the conditions that prevailed there and gave rise to their characteristic chemical and mineralogical composition and structures. These primitive rocks are messengers from the outer space that carry with them precious secrets about the formation of the Solar system, depends on us to reveal them. In this paper a review of the work done in the Centro Brasileiro de Pesquisas Físicas (CBPF/MCT), applying the Mössbauer spectroscopy to the study of the meteoritic Fe-Ni system will be reported

Les méthodes de caractérisation de l'obsidienne : datations par traces de fission et circulation de l'obsidienne dans l'Aire Septentrionale Andine préhispanique

International audienceL'obsidienne est un matériel exceptionnel par la richesse de ses possibilités de caractérisation dans les études de provenance d'artefacts archéologiques. Les méthodes actuellement en usage ou potentielles, relevant de la géochimie, de la datation, de l'étude structurale du matériau et de sa minéralogie, sont brièvement présentées. Une illustration de l'intérêt de combiner entre elles ces approches est donnée à partir de sites préhispaniques de l'Aire Septentrionale Andine, dont les obsidiennes ont été caractérisées à la fois par leur composition chimique et leur âge de formation

First characterization of obsidian from Colombian and Ecuadorian sources using ICP-AES and ICP-MS

International audience41 obsidian from geological sources of SW Colombia and Ecuador were analysed by ICP-AES and ICP-MS to contribute to the build-up of a database for obsidian provenience studies. It is shown that obsidians from the Colombian Paletara caldera (Río Hondo and Río Granates compositional groups), the Ecuadorian sierra de Guamaní (Mullumica/Callejones and Quiscatola/Yanaurcu groups) and North Cotopaxi volcano (Quebrada Colorada group) can be easily distinguished from each other. It is also shown that obsidians with a given chemical composition may be found over a large distance, up to >100 km from volcanic structures (e. g. from ignimbrites to calites in NW of Paletara caldera)

Caracterização Mineralógica e Beneficiamento do Caulim de Prado (BA)

Na região de Prado, sul da Bahia, Brasil, ocorre um importante depósito de caulim que tem sido explorado pela Mineração de Caulim Monte Pascoal desde 1992. O caulim destina-se principalmente à indústria do papel e para produção de catalisadores utilizados no craqueamaneto do petróleo. O depósito apresenta dois tipos distintos de minério. O caulim da base da sequência é de origem primária, qualidade superior e destina-se principalmente à indústria do papel. O caulim do topo é de origem sedimentar e de qualidade inferior, baixo grau de cristalinidade e alto teor de ferro e destina-se principalmente à indústria de catalisadores. O caulim foi submetido ao processo separação magnética e tratamento com agente redutor, ditionito de sódio visando elevar o índice de alvura e eliminar as impurezas mineralógicas presentes no caulim. As amostras foram caracterizadas através da difratometria de raios X, microscopia eletrônica de varredura e ressonância paramagnética eletrônica. Os espectros de RPE das amostras de caulim exibem ressonâncias paramagnéticas (g = 4,9 e 4,2) atribuídas ao Fe3+ em sítios de simetria octaedral na estrutura da caulinita substituindo o Al3+ e ressonância ferromagnéticas (g = 2,0) associadas a óxidos e/ou hidróxidos de ferro presentes em fases externas a caulinita