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Characterization of Pietra Ollare artifacts: archeometric and petrographic approaches. Conz E., Cantù M., Rebay G., Riccardi M. P. Dipartimento di Scienze.

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Presentation on theme: "Characterization of Pietra Ollare artifacts: archeometric and petrographic approaches. Conz E., Cantù M., Rebay G., Riccardi M. P. Dipartimento di Scienze."— Presentation transcript:

1 Characterization of Pietra Ollare artifacts: archeometric and petrographic approaches. Conz E., Cantù M., Rebay G., Riccardi M. P. Dipartimento di Scienze della Terra e dell’Ambiente, Università degli Studi di Pavia Pisa, 17 settembre

2 The Italian term «Pietra ollare» (from the latin olla: pot) refers to basic and ultrabasic metamorphic rocks that belong to greeschist, blueschists and eclogite facies. These rocks are very common in Alpine ophiolites. Pietra ollare…what does it mean??? Mechanical properties Good workability Fire resistant Food preserving Refractory Handmade (Iron Age) Lathe: wall thinning of containars (Augustus Age) IV century AD Increase of production in Aosta Valley V century AD Developing of pietra ollare production and trade Early Middle Ages Improving of pietra ollare working techniques 2

3 A literature review… Several studies about the characterization of «Pietra ollare» manufacts have been carried out since 70’s. Tiziano Mannoni (Mannoni, Pfeifer, Serneels, 1987) was the first to investigate the petrography and systematically classify «Pietra ollare» archeological findings, defining a classification with 11 different categories (from A to L) that are still use today. Some comparative petrochemical studies of archeological findings and stones from main production centers of the Alps have been performed. Archeological findings from Vaude and Lemie archeological sites (Torino, Italy), photos by Maurizio Rossi 3

4 Mannoni categories (Mannoni, Pfeifer, Serneels, 1987) Group A Serpentinoschists (rare in Aosta Valley) Group B Coarse grain talc-carbonate-bearing rocks containing amphiboles Group E Talcoschists containing amphiboles Group H Metagabbros Central Alps Ligurian Alps Group F Fine grain Cloritoschists Group G Coarse grain Cloritoschists Aosta Valley, Western Swizerland, Piedmont Group L «Prasiniti» albite + chlorite metabasites (rare in all the Alps) Group I Amphiboloschists Group K Olivine schists Group C Coarse grain talc-carbonate-bearing rocks Group D Fine grain talc-carbonate-bearing rocks 4

5 Valli di Lanzo pietra ollare quarries and archeological sites Tectonic sketch map of Northwestern Alps (Modified from L. PELLETIER, O. MÜNTENER, 2006, p. 113). Valli di Lanzo and location of pietra ollare quarries. 1) Bric dou Sarvaj quarry, Ala di Stura, Val d’Ala (Photo by Laura Vaschetti, 1995) Archeological sites Quarries 2) Rio Gorgia quarry, Lemie, Valle di Viù. Stone blocks (Photo by Laura Vaschetti, 2011) 3) Rio Gorgia quarry, Lemie, Valle di Viù. (Photo by Gisella Rebay, 2013)

6 Archeological findings VA/45 VA/46 VA/81 VA/28 VA/68 VA/82 Vessel shards. Late roman-early medieval settlement of San Carlo Canavese, Vaude. LE/86+95 Vessel shard. Late roman-early medieval workshop of Lemie (Valle di Viù). CA01 CA02 CA03 108:7 91:1 108:5 120:14 Semi-finisched whorl and vessel shards. Medieval mining settlement of Usseglio (Val di Viù). Samples from Bric dou Servaj quarry. Ala di Stura (Val d’Ala). CA06 Sample from Rio Gorgia quarry, Lemie (Valle di Viù). 06/07/1 6

7 Provenance and classification problems… All specimens (archeological findings and stones) belong to the group F of the Mannoni classification. All the studied specimens are fine grained green chlorite-schists. The diffusion of lithologies corresponding to group F throughout the Alps does not allow to univocally associate findings to quarries. Hand sample analysis So what? Geochemical studies Mineral and texture characterization Description of the mineral phases Morphological classification of foliations Geochemical analyses (Major and trace element) of representative mineral phases Archeological studies Charachterization of aesthetic and techical properties of the artefacts Investigation of local production centers Petrographic studies 7

8 Mineral and texture characterization VA46 2 mm chl amph 1 mm VA82 chl ttn grt px amph S1 S2 S1 chl ttn LE/ mm 1 mm CA01 grt chl S1 CA01 Bric dou Servaj, quarry, Ala di Stura LE/86+95 Workshop of Lemie VA46, VA82 Settelment of Vaude ep 8

9 Micro structural analyses MineralD1Post-D1 chl gr Op CA01 MineralD1D2Post-D2 chl Op amph ep VA46 MineralD1Post-D2 chl Op amph px gr ttn VA82 MineralD1D2Post-D2 chl Op ttn LE01 chl gr op amph ep px ttn Relative age diagrams chlorite garnet opaque amphibole epidote pyroxene titanite CA01 ≅ VA46 ≅ LE01 VA82 ??? 9

10 Geochemical analyses (major elements) Whole rock major element analyses carried out by ICP-ES Binary diagrams of major elements of chloriteschists findings and quarry samples. (Mannoni’s collection outcrops data compared with literature data of medieval artifacts and millstones). Martin et al., 2008 Santi et al., 2009 Antonelli et al., 2012 Zoppi, 2012 M6 M12 M3 Samples from St. Marcel Valley Fidings from Medieval Tuscan archeological sites Roman millstones from Aquileia Mannoni’s collection Aosta Valley quarries samples (Cervinia, Châtillon, S. Vincent, S. Jaques, Champorcher, Gressoney, Ayas, Arnad, etc.) 10

11 Geochemical analyses (minor elements) Martin et al., 2008 Santi et al., 2009 Antonelli et al., 2012 Zoppi, 2012 Whole rock trace and minor element analyses carried out by ICP-MS Binary diagrams of minor elements of chloriteschists findings and quarry samples. (Mannoni’s collection outcrops data compared with literature data of medieval artifacts and millstones). 11

12 Metodology Hand sample analysis Lithotype identification Petrographic analysis Archeological analysis Color Grain size Mineral phases (volume percentage) Color Grain size Mineral phases (volume percentage) + Cristal shape Texture Microstructural analyses Shape Size Conservation state Typological study Chronology Working traces Use traces References Archeological finding characterization Geochemical analysis Mayor and trace elements of mineral phases, selected by the micro-structural position, with SEM- EDX and LA-ICPMS Geochemical characterization Possible findings- quarries correlation Sampling in possible provenance quarries 12

13 Database 13

14 1) Mannoni’s classification is a useful tool but not enough detailed 4) It’s possible to associate a finding to a quarry in a local production system when quarries and settlements are within few km distance 5) The correlation between petrographic, geochemical and archeological analyses could be a possible way 3) Classification and provenance studies, that have been carried out since today, do not allow to univocally associate findings to quarries 2) “ Pietra ollare” lithotypes are very common in Western and Central Alps. Conclusions 14

15 15 Thanks for your attention!!! Pietra ollare Team Saint Jaques, Val d’Ayas, agosto 2012


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