Navigation – Plan du site
Articles de synthèse

A particular temper: mineralogical and petrographic characterisation of ceramic fabrics with glauconitic inclusions

Un dégraissant particulier : caractérisation minéralogique et pétrographique de pâtes céramiques à inclusions glauconitiques
Elena Basso, Claudio Capelli, Maria Pia Riccardi et Roberto Cabella
p. 93-97

Résumés

Dans cet article, on présente la caractérisation minéralogique et pétrographique des pâtes céramiques riches en pellets glauconitiques, trouvées dans quelques productions locales de sites européens et méditerranéens d’age préhistorique à médiéval. Les plus importants éléments discriminants des pellets glauconitiques sont leur forme arrondie, leur couleur rouge ou noire et leur composition chimique particulière. Durant la cuisson, comme quelques tests préliminaires sur sédiments glauconitiques l’ont confirmé, les pellets changent de couleur (de vert à rouge ou noir en lame mince), à cause de l’oxydation du fer bivalent, et leur texture devient plus homogène, jusqu’à la vitrification partielle ou totale à des températures relativement hautes.

Haut de page

Notes de la rédaction

rec. Jun. 2007 ; acc. Oct. 2008

Texte intégral

1. Introduction

1Among the various types of raw materials used in the past to produce ceramics, there are the glauconite-rich clays and sands. However, whereas glauconite-rich sediments are fairly diffused, ceramics made of these particular raw materials are little known, at least as for productions with large-scale diffusion.

2In our researches, based on thin-section analyses, we found out local productions of ceramics characterised by a temper rich in glauconitic pellets in a few European and Mediterranean sites dated from Prehistory to the Middle Ages (Fig. 1): abri Pendimoun, Castellar (Basso et al., 2006) and Villa Giribaldi, Nice (Binder et al., 1994) in the Maritime Alps, South-Eastern France (Neolithic); Isle of Malta (Bruno & Capelli, 1999; Roman age); Hérin, Northern France (Roman age, unpublished; we are grateful to R. Clotuche, INRAP, who provided the samples).

Figure 1: Localisation of the sites discussed in the text.
Figure 1 : Localisation des sites mentionnés dans le texte.

Figure 1: Localisation of the sites discussed in the text.Figure 1 : Localisation des sites mentionnés dans le texte.

3In addition, glauconitic fabrics are described in some productions (Fig. 1) of Kent, UK, dated to the Iron age (Castle Hill; Vince, 1996) and the Middle Ages (Cleeve Abbey; Vince, 1998), of North-Western France, dated to the Middle Neolithic (Vivoin; Guesquière et al., 2003) and of Southern France, dated to the Early Neolithic (Alpes Maritimes, Var; Echallier, 1991; Echallier & Courtin, 1994; Manen et al., 2006).

4Glauconite is a Fe-rich dioctahedral mica, with general formula: K(R3+1.33R2+0.67)(Si3.67Al0.33)O10(OH)2 with Fe3+ >> Al and Mg > Fe2+ (Bailey, 1980),that generally occurs in marine sediments (outer-shelf environments characterised by very slow accumulation rates and moderately reducing conditions), namely in the so-called “green sands”. It usually forms, sometimes in association with other phyllosilicates and phosphates, fine-grained rounded aggregates (“pellets”), which are green in colour when observed in thin section (Odin & Matter, 1981; Deer, Howie & Zussman, 1992).

5It must be noted that green pellets can have a high mineralogical and chemical variability and therefore accurate analyses are necessary in order to discriminate glauconite from celadonite or other phyllosilicate minerals (Bailey, 1980). However, we will use here the term “glauconitic” pellets in a general way.

6This paper will focus on the mineralogical and petrographic characterisation (by optical microscopy, XRPD and SEM-EDS) of glauconite-rich ceramic fabrics as well as on the preliminary results of a few experimental firing tests on samples of glauconite-rich sediments, which were carried out in order to highlight the textural and mineralogical changes of glauconitic pellets.

2. The distinguishing features of glauconite-rich fabrics

7When observed with the naked eye, glauconite-rich fabrics show abundant, well-sorted, spherical or ellipsoidal inclusions, which are black or dark brown in colour.

8The dimensions of glauconitic pellets in the studied ceramic pastes range from about 0.25 to 1 mm. The pellets/clay matrix ratio is variable, but textural features (the high sorting) suggest that a glauconitic sand was added to temper a fine-grained clay in most cases.

9Under the polarizing microscope, pellets are not pleochroic and their red to black colour depend on firing temperatures and redox conditions. The colour of the inclusions can vary from the core to the surface of the sherd and even differences between core and rim of individual pellets can be observed. The texture of each pellet is generally homogeneous; high-temperature black ones are vitrified and bubble-rich (Fig. 2). Fine-grained inclusions of quartz, mica and, most of all, apatite are often recognisable by the scanning electron microscope.

Figure 2: Thin section examples of glauconitic pellets in ceramic fabrics fired at medium (left) and high (right) temperatures (parallel polars; samples from the Isle of Malta).
Figure 2 : Exemples en lame mince de pellets glauconitiques dans des pâtes céramiques cuites à temperatures moyennes (à gauche) et hautes (à droite) (nicols parallèles; échantillons provenant de l’Ile de Malte).

Figure 2: Thin section examples of glauconitic pellets in ceramic fabrics fired at medium (left) and high (right) temperatures (parallel polars; samples from the Isle of Malta).Figure 2 : Exemples en lame mince de pellets glauconitiques dans des pâtes céramiques cuites à temperatures moyennes (à gauche) et hautes (à droite) (nicols parallèles ; échantillons provenant de l’Ile de Malte).

10It must be stressed that, in general, X-ray diffractometry was not useful to recognise the presence of glauconite in the ceramic pastes. The lack of characteristic peaks could be explained not only by the strong modifications of glauconite during the firing processes (already at about 375 °C, the oxidation of the divalent iron accompanied by partial loss of hydroxyls takes place; Dekeyser, 1955), but also by the reactions with some associated minerals, which might reduce the thermal stability field of glauconite and favour the partial or total vitrification of the pellet.

3. Firing tests on glauconitic sediments

11A few experimental pastes were made by mixing 30% of glauconitic pellets to a clay. Neocomian glauconite-rich layers and marls outcropping at the bottom of the rock shelter covering the Pendimoun site, SE France, were used. The glauconite-rich layers consist of abundant glauconitic pellets included in a very fine-grained matrix. Pellets are spherical or ellipsoidal in shape, with a diameter ranging from 50 to 700 µm, depending on the position within the sampled layer: the coarser pellets are at the bottom. A green-coloured clayey matrix binds the pellets and the pellets/clay ratio is quite variable. Under the polarising microscope, pellets are inhomogeneous and include apatite grains. They are generally bright green in colour.

12Test samples were square-moulded (4x4x0.5 cm) and fired in a muffle furnace under oxidising atmosphere at maximum T =  500°, 600°, 700° and 800°C (kept for 14 hours). The major visible effects of the temperature increase are the change in colour of glauconitic pellets (from green to yellow-orange and then to dark red-brown due to the oxidation of divalent iron) and the progressive homogenisation of their texture (Fig. 3). Further XRD analyses will be carried out in order to focus on the mineralogical changes.

Figure 3: Particulars in thin section of firing tests on a clay tempered with glauconitic pellets (parallel polars).
Figure 3 : Détails en lame mince de tests de cuisson sur une argile mélangée avec un sable glauconitique (nicols parallèles).

Figure 3: Particulars in thin section of firing tests on a clay tempered with glauconitic pellets (parallel polars).Figure 3 : Détails en lame mince de tests de cuisson sur une argile mélangée avec un sable glauconitique (nicols parallèles).

4. Discussion and conclusions

13Thin section and, only in some difficult cases, SEM-EDS analyses allow us to distinguish, in ceramic pastes, glauconitic inclusions from others that can be quite similar macroscopically, such as Fe-oxides, chamotte, volcanic rock fragments or mafic minerals. Instead, fired glauconite cannot be recognised by XRD analyses.

14Colour changes of glauconitic pellets from green to red or black depend on the temperature increase and oxidising conditions inside the kiln.

15As in particular for ceramics fired at high temperatures, the loss of optical characteristics due to vitrification processes can make glauconitic pellets look like Fe-oxides/hydroxide nodules, but microchemical analyses show as the former are mainly disinguished by lower Fe/Si ratios and major quantities of K (Fig. 4).

Figure 4: SEM images and EDS analyses of a glauconitic pellet (top) and a Fe-rich nodule (bottom) included in ceramic fabrics from abri Pendimoun.
Figure 4 : Images au MEB et analyses SDE d’un pellet glauconitique (en haut) et d’un nodule riche en fer (en bas) inclus dans des pâtes céramiques provenant de l’abri Pendimoun.

Figure 4: SEM images and EDS analyses of a glauconitic pellet (top) and a Fe-rich nodule (bottom) included in ceramic fabrics from abri Pendimoun.Figure 4 : Images au MEB et analyses SDE d’un pellet glauconitique (en haut) et d’un nodule riche en fer (en bas) inclus dans des pâtes céramiques provenant de l’abri Pendimoun.

16With the naked eye, glauconitic fabrics could also be confused with some ceramic pastes rich in volcanic rock and mineral inclusions (augitic clinopyroxene in particular), which are typical of several Roman wine amphorae and coarse wares productions of Central and Southern Italy, largely diffused in the Mediterranean area and in Europe as well (Thierrin-Michael, 1990). However, under the microscope the textural and mineralogical differences are obvious.

17In conclusion, ancient European and Mediterranean ceramic productions made from glauconite-rich raw materials are not abundant. Moreover, the diffusion range of these productions is quite limited. However, it is important to recognise glauconite temper, in order to avoid misleading archaeological interpretations about production, provenance and trades.

Haut de page

Bibliographie

Bailey, S.W., 1980. Summary of recommendations of AIPEA nomenclature committee on clay minerals. Am. Mineral., 65: 1-7.

Basso, E., Binder, D., Messiga, B. and Riccardi, M.P., 2006.The Neolithic pottery of abri Pendimoun (Castellar, France): a petro-archaeometric study. In Maggetti, M., Messiga, B. (eds.), Geomaterials in Cultural Heritage. Geological Society, London, Special Publications, 257: 33-48.

Binder, D., Gassin, B. and Sénépart, I., 1994.Éléments pour la caractérisation des productions céramiques néolithiques dans le Sud de la France. L’exemple de Giribaldi. InTerre Cuite et Société. La céramique, document technique, économique, culturel. XIV Rencontres Internationales d’Archéologie et d’Histoire d’Antibes, Ed. APDCA, Juan-les-Pins, 255-267.

Bruno, B. and Capelli, C., 1999. Nuovi tipi di anfore da trasporto a Malta. In D’Amico, C. and Tampellini, C. (eds), Atti della 6a Giornata: Le Scienze della Terra e l’Archeometria, Grafica Atestina, Este, 59-65.

Deer, W.A., Howie, R.A. and Zussman, J., 1992.An introduction to the rock-forming minerals. Longman,  London.

Dekeyser, W., 1955. Clay-Mineral Research in Belgium (1945-1955). Clays and Clay Minerals, 4: 158-160.

Echallier, J.-C., 1991. La céramique. In Binder D. (ed.), Une économie de chasse au Néolihique ancien. La grotte Lombard à Saint-Vallier-de Thiey (Alpes-Maritimes), Monographie du Centre de Recherches Archéologiques, 5, Paris, ed. du CNRS, 71-89.

Echallier, J.-C. and Courtin J., 1994. Approche minéralogique de la poterie du Néolitique ancien de la Baume de Fontbrégoua à Salernes (Var). Gallia Préhistorie, 36: 267-297.

Guesquière, E., Marcigny, C., Aubry, B., Clément-Sauleau, S., Dietsch-Sellami, M.-F., Deloze, V., Hamon, G., Guerré, G. and Renault, V., 2003. L’habitat néolithique moyen I de Vivoin le Parc (Sarthe). Bulletin de la Société Préhistorique Française, 100, (3): 533-574.

Manen, C., Convertini, F., Binder, D., Beeching, A., Briois, F., Bruxelles, L., Guilaine, J. and Sénépart, I., 2006. Premier résultats du projet ACR “Productions céramiques des premières sociétés paysannes”. L’exemple des faciès impressa du Sud de la France. In Fouéré, P., Chevillot, C., Courtaud, P., Ferullo, O., Leroyer, C. (eds.), Paysages et Peuplements. Aspects culturels et chronologiques en France méridionale. Actualité de la recherche, Actes des Sixièmes Rencontres Méridonales de Préhistoire Récente, Périgueux, 2004, Association pur le Développement de la Recherche Archéologique et Historique en Périgord, Préhistoire du Sud-Ouest, Périgueux, suppl. 11: 233-246.

Odin, G.S. and Matter, A., 1981. De glauconarium origine. Sedimentology,  28: 611-624.

Thierrin-Michael, G., 1990. Roman wine amphorae: Production sites in Italy and imports to Switzerland. In Pernicka, E., Wagner, G.A. (eds.), Archaeometry ‹90, Birkhauser Verlag Basel, 523-532.

Vince, A., 1997. Petrological analysis of some Iron Age pottery from Kent, AVAC Reports 1997/007 Lincoln, Alan Vince Archaeology Consultancy. From http://www.postex.demon.co.uk/.

Vince, A., 1998. The Petrology and ICPS Analysis of the Medieval Floor Tiles from Cleeve Abbey, Somerset. From http://www.postex.demon.co.uk/reports/cleeve/frames.htm.

Haut de page

Table des illustrations

Titre Figure 1: Localisation of the sites discussed in the text.Figure 1 : Localisation des sites mentionnés dans le texte.
URL http://archeosciences.revues.org/docannexe/image/1001/img-1.png
Fichier image/png, 40k
Titre Figure 2: Thin section examples of glauconitic pellets in ceramic fabrics fired at medium (left) and high (right) temperatures (parallel polars; samples from the Isle of Malta).Figure 2 : Exemples en lame mince de pellets glauconitiques dans des pâtes céramiques cuites à temperatures moyennes (à gauche) et hautes (à droite) (nicols parallèles; échantillons provenant de l’Ile de Malte).
URL http://archeosciences.revues.org/docannexe/image/1001/img-2.jpg
Fichier image/jpeg, 484k
Titre Figure 3: Particulars in thin section of firing tests on a clay tempered with glauconitic pellets (parallel polars).Figure 3 : Détails en lame mince de tests de cuisson sur une argile mélangée avec un sable glauconitique (nicols parallèles).
URL http://archeosciences.revues.org/docannexe/image/1001/img-3.jpg
Fichier image/jpeg, 1,2M
Titre Figure 4: SEM images and EDS analyses of a glauconitic pellet (top) and a Fe-rich nodule (bottom) included in ceramic fabrics from abri Pendimoun.Figure 4 : Images au MEB et analyses SDE d’un pellet glauconitique (en haut) et d’un nodule riche en fer (en bas) inclus dans des pâtes céramiques provenant de l’abri Pendimoun.
URL http://archeosciences.revues.org/docannexe/image/1001/img-4.jpg
Fichier image/jpeg, 705k
Haut de page

Pour citer cet article

Référence papier

Elena Basso, Claudio Capelli, Maria Pia Riccardi et Roberto Cabella, « A particular temper: mineralogical and petrographic characterisation of ceramic fabrics with glauconitic inclusions », ArcheoSciences, 32 | 2008, 93-97.

Référence électronique

Elena Basso, Claudio Capelli, Maria Pia Riccardi et Roberto Cabella, « A particular temper: mineralogical and petrographic characterisation of ceramic fabrics with glauconitic inclusions », ArcheoSciences [En ligne], 32 | 2008, mis en ligne le 31 décembre 2011, consulté le 24 septembre 2017. URL : http://archeosciences.revues.org/1001 ; DOI : 10.4000/archeosciences.1001

Haut de page

Auteurs

Elena Basso

Dipartimento di Scienze della Terra – Università degli Studi di Pavia, Via Ferrata 1, 27100 Pavia. CENISCO – Centro Interdisciplinare per lo Studio e la Conservazione dei Beni Culturali, Dipartimento di Studi Umanistici – Università del Piemonte Orientale “A. Avogadro”, Via A. Manzoni 8, 13100 Vercelli.elena.basso@manhattan.unipv.it

Claudio Capelli

Dipartimento per lo Studio del Territorio e delle sue Risorse –Università degli Studi di Genova, Corso Europa 26, 16132 Genova.capelli@dipteris.unige.it

Articles du même auteur

Maria Pia Riccardi

Dipartimento di Scienze della Terra – Università degli Studi di Pavia, Via Ferrata 1, 27100 Pavia. CISRiC - Centro Interdipartimentale di Studi e di Ricerche per la Conservazione dei Beni Culturali – Università degli Studi di Pavia, via Abbiategrasso 207, 27100 Pavia.riccardi@crystal.unipv.it

Roberto Cabella

Dipartimento per lo Studio del Territorio e delle sue Risorse –Università degli Studi di Genova, Corso Europa 26, 16132 Genova.

Articles du même auteur

Haut de page

Droits d’auteur

Article L.111-1 du Code de la propriété intellectuelle.

Haut de page