Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – 2015
ARCHAEOMETRY OF TRACHYTE FROM THE EUGANEAN HILLS (NE ITALY):
PROVENANCE QUARRY RECOGNITION AND WEATHERING ANALYSIS
Ph.D. candidate: LUIGI GERMINARIO, 2nd course
Tutor: Prof. CLAUDIO MAZZOLI
Co-Tutor: Dr. LARA MARITAN
Cycle: XXIX
Abstract
Trachyte from the Euganean Hills has been historically used in northern and central Italy as raw material for artifacts
and building stone for numerous monuments, infrastructures and private construction, especially since the Roman times. The
recognition of the quarry from which the stone used in cultural heritage was extracted provides clues about ancient trades,
quarrying and sources of stone supply. This research proposes new petrographic and geochemical criteria for recognizing the
provenance quarry of Euganean trachyte, based on its associations of mineralogical, textural and microchemical characteristics. In the next phase, the study will investigate short- and long-term alterations of trachyte in polluted urban contexts, exploring the rate and type of weathering, the influence of exposure point and the connection with environmental conditions. This is
demanded by air quality-related issues for the conservation of trachyte used in the built environment.
Introduction
The Euganean Hills are the most important quarry district in Italy for the extraction of trachyte, a subvolcanic rock dated to the lower Oligocene (De Pieri et al., 1983; Zantedeschi, 1994) extensively exploited in more than 70 open-pit quarries. This intense exploitation activity is related to the wide use of trachyte in cultural heritage, as raw material for artifacts and building stone for numerous monuments, infrastructures and private construction, until present times, thanks to its durability and excellent technical
properties. Its use in historical times spread in northern and central Italy, especially during the Roman period, using trades in the Adriatic Sea and channels and rivers in the Venetian Plain (Capedri et al., 2000).
This study involves two main lines of research regarding the archaeometry of Euganean trachyte:
1) The former addresses the definition of new petrographic and geochemical criteria for recognizing the
provenance quarry of the stone used in ancient buildings and artifacts, based on its distinctive associations
of mineralogical, textural and microchemical characteristics. This will provide clues about ancient trades,
quarrying and sources of stone supply. A new reference database is under preparation, and will provide a
new experimental approach to provenance studies, alternative to that developed by Capedri et al. (2000),
which often has proved to be not sufficiently reliable (Maritan et al., 2013). The new approach will be
used in the provenancing of a set of Roman archaeological samples.
2) The latter focuses on the short- and long-term alteration of trachyte used in historical buildings in polluted urban contexts. For this, the rate and type of stone weathering, the influence of the specific location
and the correlation with environmental conditions will be explored with a multianalytical approach. This
is demanded by air quality-related issues for the conservation of trachyte used in the built environment
and the lack of systematic studies about this subject (Valluzzi et al., 2005; Lazzarini et al., 2008).
This research has addressed the first topic so far.
Materials and methods
An extensive sampling of trachyte was performed in the entire area of the Euganean Hills, in about 40
quarries, and samples were analyzed by: optical microscopy (OM), scanning electron microscopy with
energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray fluorescence (XRF) and electron probe microanalyzer (EPMA). Moreover, micro X-ray fluorescence (µ-XRF) was applied at the Department of Earth
Sciences of the University of Torino. Finally, analyses by laser ablation inductively-coupled plasma mass
spectrometry (LA-ICP-MS) were performed at Micro Analysis Facility of Bruneau Centre for Research
and Innovation, Memorial University of Newfoundland (Canada). The data were processed through a bi1
Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – 2015
variate and multivariate statistical analysis, combining principal component analysis (PCA), discriminant
analysis and cluster analysis, in order to find the most distinctive petrographic and geochemical parameters among the quarries.
Preliminary results and discussion
The comparison of the OM observations and geochemical XRF data – techniques traditionally used in
provenance studies of Euganean trachyte – with the reference database of Capedri et al. (2000) confirmed
the substantial inadequacy of this approach in accurately discriminating all the quarry localities in the Euganean district. Indeed, there is not enough variability in terms of petrographic features, evaluated on a
qualitative basis, and bulk chemical composition among the trachytes from different outcrops. Their attribution to a precise quarry is possible with good precision only for few sites, and only combining the
two techniques. Concerning the microscopic observations, the main drawback is that a complete collection of trachyte quarry samples of known provenance is needed in order to allow a direct comparison with
an unknown sample. With regard to XRF data, their statistical analysis provided few chemical-element
pairs useful for provenance clustering, e.g. V/Nb, TiO2/Zr, TiO2/K2O, Na2O/Zr, Rb/Zr, Al2O3/Sr and
Ce/Nd, but these are not totally effective for all the Euganean quarries (Fig. 1). Moreover, data can be
heavily affected by experimental conditions, such as statistical and compositional representativeness of
the samples, as confirmed by the discrepancy between the results obtained in this study and those constituting the reference database presently available from literature (Capedri et al., 2000). When analyzing
archaeological materials, XRF is usually applied to small samples, which are not representative enough of
the bulk chemical composition of the outcrops they come from. Furthermore, surface alteration may affect the results as well.
This evidence was also confirmed by OM and XRF analyses of a set of archaeological samples of trachyte, from most of the known Roman infrastructures (roads, bridges) in Veneto, in the frame of an interdisciplinary research collaboration with the Department of Cultural Heritage of the University of Padova.
Fig. 1. V/Nb scatterplot from the XRF data
obtained from all the Euganean quarry localities sampled.
The alternative approach proposed here involves the determination of quantitative petrographic properties
by µ-XRF and SEM-EDS mapping coupled to image analysis, and that of microchemical composition of
specific mineral phases by LA-ICP-MS supported by EPMA.
Mineralogical and textural information on phenocrysts derived from µ-XRF mapping, while that referred
to microlites in the groundmass from SEM-EDS mapping (Fig. 2). The digital image analysis of X-ray
maps allowed the calculation of the relative abundance of each mineral phase, its size and shape properties (Feret diameter, area, perimeter, circularity and aspect ratio), crystal size distribution and phenocrysts-groundmass ratio. The preliminary data processing indicates that the various trachyte quarries can
be distinguished on the basis of: 1) presence, abundance, size and distribution of feldspar phenocrysts; 2)
phenocrysts-groundmass ratio; 3) composition, size and shape of feldspar microlites in the matrix; 4)
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – 2015
presence and abundance of intercrystalline glass and cristobalite. The PCA of these parameters further
supports the possibility to effectively differentiate quarries.
The LA-ICP-MS results provided the trace-elemental composition of all the major mineral phases, determined on about 500 different phenocrysts of anorthoclase, plagioclase, sanidine, biotite, augite, kaersutite, Ti-magnetite and apatite. While EPMA major-element composition of a given phase resulted rather
homogeneous among all the samples also from different quarries, the concentrations of trace elements resulted to be an effective discriminating tool. From the preliminary data analysis – carried out so far on the
main quarry localities of the antiquity (Previato et al., 2014) – microchemistry of feldspars and concentration of rare earth elements (REE) can provide a satisfactory clustering among the quarries, as also confirmed by PCA (Fig. 3); in particular, a differentiation in concentration of LREE (light REE) and HREE
(heavy) can be identified as a good parameter for distinguishing provenance.
Fig. 2. Classified maps of samples from Monselice (left), M. Merlo (center) and M. Oliveto (right), after X-ray mapping by µ-XRF (top) and
SEM-EDS (bottom). Different colors indicate different phases, as shown in legend (field size µ-XRF: 5.30x4.14 cm; SEM: 800x640 µm).
Fig. 3. Score plot from a PCA performed on traceelement composition (Li, P, Ti, V, Ni, Cu, Zn, Rb,
Sr, REE) of anorthoclase phenocrysts in trachyte
samples from Monselice, M. Merlo and M. Oliveto.
PC1 and PC2 cover 33% and 26% of total variance
respectively.
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – 2015
Even though the data are still being processed, this novel experimental approach seems to provide more
reliable criteria for quarry recognition than traditional methods, so that it might allow a precise provenance study in a micro-destructive way, with the analysis of very limited amounts of material from the
object to be investigated, virtually on a single thin section.
Future research plan
The work planned for the next year will firstly involve a deeper and more complete statistical analysis of
the data acquired so far, in order to definitely find the best petrographic and geochemical parameters suitable for provenancing. The new criteria will be used to determine with higher accuracy the provenance of
the Roman archaeological samples, providing solid constraints to the reconstruction of ancient trades, viabilities and territorial organization of settlements, and comprehension of the mechanisms of circulation
of raw and finished stone materials during the Roman times.
The second line of research will address the weathering analysis of Euganean trachyte in polluted urban
contexts through the investigation of its short- and long-term alterations. Short-term alterations will be
studied on monumental works in which trachyte has been restored and cleaned in the last 10-20 years
(e.g. in the 16th century gates of Padova) or installed as replacement material (e.g. in the cathedrals of Cologne and Xanten in Germany, Graue et al., 2011). Long-term alterations will be studied on stones originally installed in historical buildings in Veneto and never restored (e.g. in the 16th century wall system of
Padova). On-site portable techniques, such as colorimetry, XRF, laser-induced breakdown spectroscopy
(LIBS) and Fourier transform infrared spectroscopy (FT-IR) will be applied, beside laboratory sample
analyses, such as LA-ICP-MS, EPMA, gas chromatography mass spectrometry (GC-MS), XRF, environmental SEM (ESEM) and micro-Raman. Globally, the weathering will be analyzed referring to its rate
and type (composition, stratigraphy, thickness etc.); the influence of exposure point of stone in the fabric
(exposure to sunlight, washing out, height from the ground etc.) and the connection of decay with climate
and air quality conditions will be explored as well. The instrumentation will be mostly provided by the
Geoscience Center of Georg-August-Universität Göttingen, while a part of the portable setup (LIBS and
FT-IR) will be provided by the Department of Chemical Sciences of the University of Padova.
References
CAPEDRI, S., VENTURELLI, G. and GRANDI, R. 2000. Euganean trachytes: discrimination of quarried sites by petrographic and chemical parameters and by magnetic susceptibility and its bearing on the provenance of stones of ancient artefacts. J
Cult Herit, 1, 341–364.
DE PIERI, R., GREGNANIN, A. and SEDEA, R. 1983. Guida alla escursione sui Colli Euganei. Mem Soc Geol Ital, 26, 371–
381.
GRAUE, B., SIEGESMUND, S. and MIDDENDORF, B. 2011. Quality assessment of replacement stones for the Cologne Cathedral: mineralogical and petrophysical requirements. Environ Earth Sci, 63, 1799–1822.
LAZZARINI, L., ANTONELLI, F., CANCELLIERE, S. and CONVENTI, A. 2008. The deterioration of Euganean trachyte in
Venice. 153–163. In: LUKASZEWICZ J.W., NIEMCEWICZ P. (eds) Proceedings of the 11th International Congress on Deterioration and Conservation of Stone, Torun, Poland, 15–20 September 2008. Nicolaus Copernicus University, Torun.
MARITAN, L., MAZZOLI, C., SASSI, R., SPERANZA, F., ZANCO, A. and ZANOVELLO, P. 2013. Trachyte from the Roman aqueducts of Padua and Este (north-east Italy): a provenance study based on petrography, chemistry and magnetic susceptibility. Eur J Mineral, 25, 415–427.
PREVIATO, C., BONETTO, J., MAZZOLI, C. and MARITAN L. 2014. Aquileia e le cave delle regioni alto-adriatiche: il caso della trachite euganea. 149–166. In: BONETTO J., CAMPOREALE S., PIZZO A. (eds). Arqueología de la construcción IV. Las
canteras en el mundo antiguo: sistemas de explotación y procesos productivos. CSIC, Mérida.
VALLUZZI, M.R., MAZZOLI, C., MARITAN, L., BIANCHINI, G. and ANDREOLI, F. 2005. Experimental analyses for the
preservation of trachyte pavings in salt-controlled weathering conditions. 1–10. In: BANTHIA N., UOMOTO T., BENTUR A.,
SHAH S.P. (eds). Construction materials: proceedings of ConMat ’05 and Mindness Symposium, Vancouver, 22–24 August
2005. University of British Columbia, Vancouver.
ZANTEDESCHI, C. 1994. New Rb-Sr radiometric data from Colli Euganei (North-Eastern Italy). Mem Sci Geol, 46, 17–22.
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – 2015
SUMMARY OF ACTIVITY IN THIS YEAR
Courses and seminars:
- R. LEARDI, M. CALDERISI: “Analisi multivariata dei dati”, Dip. Geoscienze, Università degli Studi di Padova.
- A. BORGHI: “Le cave di pietra dell’Antico Egitto”, 28/01/2015, Dip. Beni Culturali, Università degli Studi di Padova.
Schools and congresses:
- International Summer School “ENVIMAT 2015 – Preventive conservation of monuments and archaeological sites in the
Mediterranean Basin”, 30 June–2 July 2015, IUSS, Università degli Studi di Ferrara.
- Congresso congiunto SIMP-SGI-SoGeI-AIV “Il pianeta dinamico: sviluppi e prospettive a 100 anni da Wegener”, 2–4 September 2015, Università degli Studi di Firenze.
- Scuola di spettroscopia infrarossa applicata alla diagnostica dei beni culturali – IV edizione “Focus: le altre spettroscopie.
Spettroscopia Raman”, (planned in 9–12/11/2015), Centro per la Conservazione ed il Restauro dei Beni Culturali “La Venaria
Reale”.
Publications:
- GERMINARIO, L., COSSIO, R., MARITAN, L., BORGHI, A. and MAZZOLI, C. 2015. Textural and mineralogical analysis of volcanic rocks by µ-XRF mapping. Microchemical Journal (submitted).
Abstracts:
- GERMINARIO, L., COSSIO, R., MAZZOLI, C., MARITAN, L. and BORGHI, A. 2015. Combining µ-XRF and SEMEDS mapping in low and high resolution for determining the provenance quarry of volcanic porphyritic stones, Plinius, 41,
443. In: Congresso congiunto SIMP-SGI-SoGeI-AIV, 2–4 September 2015, Firenze, Italy
- SANTELLO, L., MARITAN, L., MAZZOLI, C., GERMINARIO, L., NESTOLA, F., HANCHAR, J.M. and USAI, D.
2015. Multianalytical characterisation of Egyptian Flint as a means for understanding seasonality in the Nile valley and Western Desert (Egypt), Plinius, 41, 458. In: Congresso congiunto SIMP-SGI-SoGeI-AIV, 2–4 September 2015, Firenze, Italy
- GERMINARIO, L., COSSIO, R., MAZZOLI, C., MARITAN, L. and BORGHI, A. 2015. Provenance study of volcanic
stones by texture analysis: a novel application of µ-XRF imaging. In: Technart 2015 – Non-destructive and microanalytical
techniques in art and cultural heritage, 27–30 April 2015, Catania, Italy
Teaching activities:
- Junior tutor: 50 hours, assistance during optical microscopy laboratory of the course “Petrografia e laboratorio di analisi
petrografiche”, Laurea triennale in Scienze Geologiche, 2015/2016 (in progress).
- Coordinator junior tutor: 15 hours, Laurea triennale in Scienze Naturali, 2015/2016 (in progress).
Other:
- Visiting PhD student, supervised by Prof. J.M. Hanchar, at the Department of Earth Sciences and Bruneau Centre for Research and Innovation, Memorial University of Newfoundland, Canada (March–June 2015).
- Grant received from SIMP for attending the conference “Congresso congiunto SIMP-SGI-SoGeI-AIV – Il pianeta dinamico:
sviluppi e prospettive a 100 anni da Wegener”, 2–4 September 2015.
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