The Mineralogical Study of the Sialk III Ceramics in the Zayanderud Watershed

Abstract
Petrographic analysis involves the identification of rocks and minerals within the clay and the examination of their relationship to geological resources compatible with archaeological evidence. This method is one of the approaches used to study ceramic materials to identify their components, recognize similarities and differences in composition, determine the proportion of each component, estimate the firing temperature of the pottery, and ultimately investigate the provenance of the raw materials used in pottery production. Given the importance of this method in archaeology and the strong similarity between pottery samples from the Zayanderud watershed and those of the Sialk III tradition at Tepe Sialk, the present research aims to investigate and analyze their characteristics. The main objectives of this study are to examine the composition and proportion of elements within the ceramic fabric, identify firing techniques and temperatures, determine similarities and differences among the samples, and explore their relationship with pottery production at Sialk. The ceramic materials examined in this study date between 4300 and 3100 BC. In total, 43 sherds were analyzed, including 36 samples from the sites of Gorgai, Ashna, Jamalo, Gavyaran, Maidanak 1, and Badarkhani, and 7 samples from Tepe Sialk. The samples were first examined based on macroscopic features, style, and surface characteristics. Petrographic analysis was then carried out using polarized light microscopy under plane-polarized light (PPL) and cross-polarized light (XPL). The results indicate that, despite minor differences in some samples, the pottery assemblages are highly similar not only in appearance and decorative motifs but also in technical characteristics such as voids, fabric structure, mineralogy, binding material, and firing temperature. Differences in the firing conditions of some Sialk samples, as well as the presence of igneous rock fragments or chert in certain cases, suggest a different origin for the production of some vessels. Nevertheless, the pottery from the Zayanderud watershed is generally influenced by Sialk III–type pottery from Tepe Sialk.
Keywords: Mineralogy, Ceramic, Chalcolithic, Sialk III, Zayanderud. 
 
Introduction
The Zayandehrud River originates from the northeastern side of the Bakhtiari mountains, specifically at the foot of the Karkonan Mountain in Chelgerd. Along its 360 km course to its mouth, numerous small and large tributaries flow into the river. The Zayandehrud Dam has a catchment area of approximately 4,262 square kilometers, situated within geographical coordinates of 54°49’ to 50°45’ East longitude and 32° 18’ to 33° 12’ North latitude. This basin, located in the Zagros highlands, features a variety of elevations and lowlands. The highest point in the basin is Karpoosh Mountain, situated in the southwest, which rises to an elevation of 3,974 meters. In contrast, the lowest point is the riverbed at the Zayandehrud Dam, at an elevation of 1,976 meters above sea level. The average elevation of the basin is 2,492 meters, and over 50% of its surface area lies at altitudes exceeding 2,400 meters. This basin is among the highest in the country, with substantial snowfall and rainfall constituting its main climatic characteristics. The earliest evidence of human occupation along the river has been identified in Qaleh Bozi Cave, located southwest of Isfahan near Dizicheh. The ancient sites within the studied basin reveal the settlement of many populations that closely followed the Sialk tradition. One of the most important environmental aspects in these areas is their nearness to the Zayandehrud River, suggesting a significant reliance on agriculture by the residents. Most of the identified locations within this basin have been cataloged through surface surveys and are attributed to the Chalcolithic period; these encompass Tepe Jamalo, Ashna, East Kalbali, West Kalbali (Jahangir Khan), Khersank 1, Gorgai Tepe, Dolatabad, Maidandak 1, Tepe Gavyaran, Tepe Nanadegan, and Badrkhani. This study examines 36 pottery sherds from the Sialk III period collected from six sites located in the Chaharmahal and Bakhtiari and Isfahan provinces. In addition, seven Sialk III–period pottery sherds from Tepe Sialk in Kashan were selected for petrographic analysis. The primary aim of these analyses is to identify the constituent materials of the ceramics and to assess similarities and differences in their composition. Specifically, the study seeks to determine the proportion of each component, estimate firing temperatures based on mineralogical evidence, and investigate the provenance of the raw materials used in pottery production. Petrographic analysis focuses on identifying the rocks and minerals within the clay matrix and evaluating their relationship to available geological resources in accordance with archaeological evidence.
 
Discussion
In this section, we analyze the questions, evaluate the research hypotheses, and draw conclusions based on the results of the experiments conducted on the data. This approach offers a different perspective on the presented content. The pottery of the Sialk III period is markedly more refined and carefully manufactured than that of the preceding Sialk II phase, which is associated with the Cheshmeh Ali culture. It can be divided into two main categories: coarse and fine wares. Coarse pottery is characterized by a paste rich in calcite and iron compounds, producing a heterogeneous, silty texture. In contrast, fine wares, which make up the majority of the assemblage, exhibit a cleaner paste with minimal impurities. Fine pottery is primarily composed of quartz minerals and iron compounds, with only minor amounts of calcite, resulting in a uniform clay–carbonate fabric. Petrographic analysis shows that the pottery from Gorgai Tepe, together with samples from Ashna, Gavyaran, and all specimens from Maidanak 1, display a fine-grained or homogeneous silty texture. In contrast, the samples from Gorgai Tepe (15), Ashna (5), Gavyaran (1 and 6), Badrkhani (2, 3, and 5), Jamalo (3, 4, and 9), and Sialk (2) showcase a fine-grained or heterogeneous silty texture, characterized by large pieces of calcite and quartz as fillers. In addition to the clay paste, inclusions such as quartz, calcite, iron oxides, and, in some cases, chert and siltstone are present as tempering materials in the pottery. Quartz is consistently the dominant component in all samples and appears to function as the principal binding material. According to reports from Sialk, the most common ceramic forms of the third period include bowls, jars, flat-based cups with vertical walls, wide-mouthed cups and bowls with bases, tubular vessels, and zoomorphic containers. Nevertheless, given the limited number of sherds examined—most of which derive from vessel bodies and include only a small proportion of Sialk-type pottery—it is not methodologically sound to reconstruct vessel forms on this basis. All samples contain quartz minerals, iron compounds, and calcite, although the relative proportions of these constituents vary within the clay matrix. Such variation is expected in light of the close geographic proximity of the sites and their broadly similar geological settings. A notable exception, however, is observed in the Gorgai samples, which contain chert inclusions, suggesting a different raw material source. Furthermore, the presence of igneous rock fragments within the clay paste from Sialk Hill indicates that this sample was derived from sediments of igneous origin. The occurrence of igneous formations in the region and the associated sedimentary deposits further support the interpretation that this clay type is of local, indigenous origin.
 
Conclusion 
This research focuses on examining the composition and relative proportions of elements within the ceramic fabrics dated to 4300–3100 B.C. A total of 43 sherds were analysed, including 36 samples from the sites of Gorgai, Ashna, Jamalo, Gavyaran, Maidanak 1, and Badarkhani, as well as 7 samples from Tepe Sialk. The main objectives of the study are to investigate production techniques, firing methods, and the level of heat required during manufacture, to identify similarities and differences among the samples, and to clarify their relationship with ceramic production at Sialk. The study addresses the following question: what are the technical and morphological characteristics of Sialk III pottery from the Zayandehrud basin? This includes an analysis of the elemental composition and its proportions within the ceramic matrix, the firing techniques employed, and the temperatures reached in the kiln during the production process. In addition, the research aims to identify the principal similarities and differences between Sialk III pottery from the Zayandehrud basin and comparable examples from the Sialk site itself. Comparative microscopic analysis of Sialk III pottery from the basin indicates a high degree of similarity with samples from Tepe Sialk in terms of surface appearance and decorative patterns. Moreover, the technical characteristics of the ceramics, including fabric composition and firing conditions, are largely consistent between the two assemblages. Despite minor variations observed among certain samples, characteristics such as voids, internal structure, mineralogical composition, binding materials, and firing temperatures display a high degree of consistency. The kneading techniques and overall paste quality are likewise comparable across the assemblage. Although individual examples show slight differences, the majority share a broadly similar fabric and structural composition. The principal constituents of the pottery are quartz, calcite, and iron oxides, with quartz functioning as the dominant binding material. Furthermore, in most samples—excluding those from Tepe Sialk—the firing temperature appears to have been below or close to 800 °C. The differences observed in the firing conditions of the Sialk samples, along with the presence of igneous rock fragments or chert inclusions in some cases, suggest a distinct provenance or production context. Nevertheless, from a technical perspective, the pottery from the Zayandehrud watershed exhibits strong similarities to Sialk III ceramics. Based on these results and the overall consistency among the samples, the selection of additional specimens for further analytical testing would be beneficial in clarifying the origin of their manufacture. Such samples may be chosen either for their close structural resemblance to ceramics from other sites or for their distinctive compositional and technological characteristics.