Elsevier

Wear

Volumes 474–475, 15 June 2021, 203708
Wear

Rock physics and the circulation of Neolithic axeheads in Central Europe and the western Mediterranean

https://doi.org/10.1016/j.wear.2021.203708Get rights and content

Highlights

  • No parallels for the long-distance transport of MJH have been found in the European Early Neolithic.

  • The use of MJH during LBK was not based on its mechanical features but on social/political factors.

  • Rocks used for Neolithic axe head manufacture were usually more elastic and less hard than knapped stone materials (flints).

  • Density is a good proxy for the suitability of fine-grained rocks for axe head manufacture.

  • Amphibolic hornfels (MJH) used for axe head manufacture is inferior in quality to several Alpine high-pressure rocks.

Abstract

Slightly retrograded rocks for edge-ground tool manufacture were used in two different supply systems during recent European prehistory. Mechanical properties of five of these rock types were tested to determine if the most exploited and circulated materials were also the most adequate ones. A series of mechanical tests were chosen to characterize their hardness, elasticity, resistance to friction, and Charpy impact toughness. The results were compared with petrographic variables (mineralogical composition, density, homogeneity, grain size, anisotropy, and presence of retrogression). Subsequent correlations between the tested mechanical properties confirm that density is a good proxy to estimate hardness, elasticity, and resistance to friction of the given rocks. It emerged that the amphibolic hornfels (MJH) most used in Neolithic Central Europe and circulated over large distances was harder than most other tested rocks and compositionally more homogeneous. On a broader European scale, however, MJH is not superior in quality to Iberian gabbros. Both rocks show much poorer mechanical qualities than Alpine high-pressure meta-ophiolites, which were largely ignored by the Early Neolithic populations of Central Europe. Analogies from the Iberian Peninsula also indicate that rocks comparable in quality to MJH, and transformed into Neolithic axe heads, only circulated in an area a few hundred kilometers from their sources. Long-distance transport of MJH is thus only partially explained by its mechanical qualities and rather reflects a wide and well-functioning social and economic network established over large parts of Central Europe which has no parallels in the European Neolithic.

Introduction

Production of edge-ground tools in Neolithic Europe is outstanding in terms of the large variety of raw materials used by this technology. Amphibolite, blueschist, eclogite, nephrite, spessartite, meta-ophiolite, metadiabase, jadeitite, omphacitite, serpentinite, sillimanite, hornfels, phonolite, and siltstone are only some of the rocks shaped into axes, adzes, chisels, etc. (e.g., Refs. [[1], [2], [3], [4], [5], [6], [7], [8]]). It can be expected that these rocks entail quite different physical behaviors during the manufacture and use of axeheads. Mechanical analysis carried out so far has confirmed that rocks were more intensively exploited and distributed over wide areas depending on certain physical properties, although the relationship between these parameters does not follow a simple economic rationale [8,9].

This paper seeks to test the importance of the mechanical properties of some of these rocks exploited during the Continental European Neolithic, when edge-ground artefacts were one of the main goods integrated into wide exchange networks (e.g. Refs. [10,11]). For the first time, two markedly different Neolithic distribution strategies are compared in terms of material qualities, production, and circulation of axeheads.

One dynamic forms part of the Early Neolithic Linear Pottery culture (LBK; ca. 5500-4900 BCE) and was responsible for the supply of amphibolite/amphibolic hornfels over large parts of Central Europe. Amphibolic hornfels was amply quarried in the Jizera Mountains in northern Bohemia [12] and, according to available petrographic and chemical analyses, circulated at considerable distances, up to >650 km as the crow flies. Such work-intensive production and distribution of axeheads is unparalleled in the Early European Neolithic. In Middle and Late Neolithic times, only Alpine high pressure meta-ophiolites (HPms: jadeitites, omphacitites and eclogites) traveled over similar, or even larger distances, from their original sources in the Western Alps [11,[13], [14], [15]]. Although different ground stone materials are abundant in Central Europe [6,16], they mostly became prominent in axe production after a certain decline in the exploitation of MJH.

The second dynamic was distinctive of the Iberian Peninsula and focused on the exploitation of secondary clast deposits containing the most suitable raw materials available in each region, such as hornfels or metagabbro. Axeheads made of these rocks supplied communities in an area of up to 150–200 km from the source, and rarely circulated beyond 400–500 km [8,10]. Contrary to the situation observed in Central Europe, these networks remained rather stable over the whole Neolithic period.

Mechanical tests were carried out to establish how far these notably different production and circulation strategies were driven (or not) by the advantageous material qualities of the rocks transformed into axeheads. The test comprised of hardness, elastic modulus, response to friction, and impact toughness measurements. The results were also compared with data acquired earlier from Baltic (erratic) flints [17], a material also used for axe head production, but supposed to possess very different mechanical qualities than ground stone material [18]. Additionally, data available for other rocks used by Neolithic communities, such as Alpine HPms, were used for an indirect comparison with MJH (see below, and [8]). Finally, mechanical tests allowed us to determine which intrinsic (petrographic) variables of the rocks conditioned the behavior of the resulting tools.

Section snippets

Materials: petrography and provenance

The studied materials originate from what is today the Czech Republic (one lithotype from northern Bohemia) and Spain (two lithotypes from Catalonia and two from south-east Iberia). The exploitation of these raw materials has been identified based on petrographic analyses, the location of workshops, and geo-archaeological surveys (e.g. Ref. [19], for Bohemian material, [10,[20], [21], [22]], for Iberian material).

Archaeological background and artefact types

Rocks often classified in the archaeological literature as amphibolite, including MJH, were used to manufacture axes, adzes, shoe-last celts, axe-hammers, hammers, hammer stones, polishers, grinding stones, picks (see Ref. [12] for overview), and possibly other tools. Amphibolite (MJH) was mostly used during the Early and the beginning of the Middle Neolithic, above all in the LBK (ca. 5500–4900 BCE), Stroke-ornamented Ware Culture (STK; ca. 4900–4500 BCE), and Rössen Culture (ca. 4700–4400 BCE

Methods

Mechanical analyses of rocks used in prehistoric times test their behavior in front of different physical forces. So as to understand the effects of these forces on the material it is necessary to distinguish between intrinsic variables and control variables [30,72]. Intrinsic variables are petrographic features inherent to each rock, while control variables quantify the resulting mechanical reaction of intrinsic variables. Therefore, each material was first described macro- and microscopically

Intrinsic variables of rocks exploited: petrographic features

The petrographic analysis of our MJH sample (Table 2; Fig. 4) shows that its texture is nematogranoblastic, with characteristic intergrowing laths and needles of radially arranged, partially chloritized amphiboles (55%; mostly actinolites). The laths reach up to 400 μm in length whereas the surrounding matrix, of grains mostly less than 10 μm in size, is composed of smaller amphiboles, plagioclases (35%), opaque minerals (10%), mostly ilmenite, and quartz as an accessory. Whereas the matrix of

Correlation between intrinsic and control variables

Correlations (Pearson's χ2 test) clearly indicate that weighted hardness is strongly acting on the mechanical properties of rocks (Table 4). Hard minerals, like quartz, garnet, or ilmenite and amphibole in MJH must have offered to the artefacts an added value especially during use, as hard particles make the tools more effective when penetrating other materials (see above). This correlation has also been noted in a frictional test of another kind Table 3 in Ref. [72]. Hard materials also tend

Conclusions and historical implications

Mechanical quality of rocks used by Neolithic communities for axe manufacture mostly derived from their density and their weighted hardness, which depends on their mineral composition, especially the amount of hard minerals. These properties are highly correlated with the mechanical hardness, the elasticity, and the resistance to friction of the rocks. Flint, which was amply used in axe production in several Atlantic regions, such as Scandinavia, South East England, North France or the Low

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was financially supported by the Ministry of Education, Youth and Sports of the Czech Republic under the project CEITEC 2020 (LQ1601), the Spanish Ministry of Economy and Competitiveness (grant number HAR2017-85962-P), the Catalan Direcció General de Recerca (grant number AGAUR 2017SGR1044), and the ICREA Academia program. We wish to thank Detlef Gronenborn for his comments on a preliminary version of the manuscript.

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