Chocolate flint: new perspectives on its deposits, mining, use and distribution by prehistoric communities in Central Europe

The discovery of previously unknown chocolate flint outcrops in the Kraków-Częstochowa Upland (only the second known area after that in the Holy Cross Mountains) has undermined our seemingly solid knowledge of the prehistoric economy, which is based on the distribution pattern of this important raw material. The authors present new interdisciplinary research focused on the prehistoric mining of chocolate flint in the Kraków-Częstochowa Upland, the distribution of chocolate flint artefacts within the Upland and beyond, and methods to distinguish this material from the Holy Cross Mountains chocolate flint.

impact on all previous interpretations regarding the use and distribution of this raw material, both on a regional and European scale. The results of our research will enable further tracking of organised intergroup contacts that are channels for exchange between distant communities.
The Chocolate Flint on the Kraków-Czestochowa Upland: Mining, Use and Distribution project, led by Magdalena Sudoł-Procyk, aims to undertake a detailed study of the spread of chocolate flint deposits in the Kraków-Czestochowa Upland area and the places of its exploitation, and to determine the role of this raw material in the prehistoric communities of Central Europe. These factors are particularly important for studies focused on the extent of the use of local raw material resources and those trying to understand the presence of material imported from distant sources in Stone Age site assemblages.

Methodology
The project applies multifaceted archaeological and geological research methods designed to recognise further chocolate flint outcrops in the area of the Kraków-Czestochowa Upland where this material was extracted and processed. Chocolate flint outcrops have been found on the eastern edge of the central part of the Kraków-Czestochowa Upland, in the Udorka Valley, near the village of Poreba Dzierzṅa. At present, this is the only known deposit of chocolate flint situated outside the Holy Cross Mountains. The Kraków-Czestochowa Upland has a monoclinal geological structure. We therefore expect that other chocolate flint-bearing outcrops will be found forming an elongated north-north-west to south-south-east belt along the eastern edge of the Kraków-Czestochowa Upland. Detailed geological mapping of these outcrops, together with studies of their geological and geomorphological context, will allow us to determine their accessibility in the past, and therefore the economic importance of these deposits for prehistoric societies.
Several prehistoric sites have been discovered in the vicinity of chocolate flint deposits within the Kraków-Czestochowa Upland area, including a flint mine and lithic workshops (   Chocolate flint: deposits, mining, use and distribution in prehistoric Central Europe Crucial in understanding the role of chocolate flint in prehistoric exchange networks is mapping its distribution on archaeological sites both in the Kraków-Czestochowa Upland area and beyond, and in neighbouring countries (Germany, Czechia, Slovakia, Hungary, Austria, Ukraine, Belarus, Lithuania). In Poland sites with chocolate flint artefacts are known from almost all periods of prehistory ( Figure 2). The exact number of sites, quantities of chocolate flint artefacts at these sites, and the character of these artefacts (knapped locally or imported as finished products), however, has never been fully evaluated. A database will be developed to record details of all chocolate flint artefacts from archaeological sites in Central Europe. This will allow a reconstruction of the prehistoric networks of chocolate flint distribution.
The efficacy of the database rests on accurate identification of chocolate flint among other silicites, and the ability to determine whether chocolate flint artefacts originate from the Holy Cross Mountains or Kraków-Czestochowa Upland sites. The success of the multi-layered chert-sourcing approach, used previously for chert materials from other parts of Europe (Brandl et al. 2018), makes it an ideal method for this task. The multi-layered chert-sourcing approach combines macroscopic grouping (by colour, rock texture and granularity), stereomicroscopic testing for group consistency (examining individual microfacies, revealing similar or dissimilar depositional environments), and geochemical analyses using LA-ICP-MS (laser ablation inductively coupled mass spectrometry). LA-ICP-MS allows for the detection of main-, trace-and ultra-trace element concentrations, which reflect past seawater chemistry, indicative of the very specific source conditions of the siliceous rocks. Geochemical results can then be statistically treated with compositional data analysis to achieve optimal clustering and therefore precise provenance information (Figure 4).

Conclusions
Accurate identification of chocolate flint from the Kraków-Czestochowa Upland area, which is macroscopically similar to that known from the Holy Cross Mountains (Schild 1971;Krajcarz et al. 2012), may provide much-needed verification of the current state of knowledge about the past distribution of this raw material. The Kraków-Czestochowa Upland outcrops might have been a particularly important source of chocolate flint for the Central European regions situated to the south and west-closer to the Kraków-Czestochowa Upland than to the Holy Cross Mountains deposit area; this could include places such as Silesia, Bohemia, Moravia, Slovakia, Bavaria, Austria or the Pannonian Basin. The identification and detailed investigation of lithic materials from archaeological sites in these regions will help to reveal the importance of both the Kraków-Czestochowa Upland and Holy Cross Mountains chocolate flint deposit areas and their wider significance in the Central European prehistoric economy.

Funding statement
The Chocolate Flint on the Kraków-Czestochowa Upland: Mining, Use and Distribution project is financed by a grant from the National Science Centre, Poland (2018/30/E/HS3/ 00567).