Archaeologia Austriaca, Band 97–98/2013–2014, 33–58 © 2014 by Österreichische Akademie der Wissenschaften, Wien doi: 10.1553/archaeologia97-98s33 33 Genesis, Provenance and Classification of Rocks within the Chert Group in Central Europe Michael Brandl Abstract hauptsächlich auf das Fehlen eines allgemein anerkannten Raw material determination of prehistoric stone tools is a Klassifikationssystems zurückzuführen, was sich auf inter- necessary analytical process towards a fuller understanding nationaler Arbeitsbasis zusätzlich verschärfend auswirkt. of prehistoric resource management. However, archaeolo- Der Hauptgrund für diesen Umstand liegt darin, dass SiO2- gists face a terminological predicament when analysing raw Modifikationen nie den Hauptfokus der Erdwissenschaf- material types present within lithic assemblages. This is ten bildeten, was zuweilen unpräzise Definitionen solcher chiefly due to the lack of a commonly accepted classifica- Rohstoffe zur Folge hatte. Die bedeutendsten SiO2-Roh- tion system, further exacerbated when working on an materialien, die prähistorisch zur Herstellung geschlagener international scale. The principle reason for this situation is Steingeräte genützt wurden, sind Silizite und gehören somit der Chert-Gruppe an, wie z. B. Chert, Flint, Radio- the fact that SiO2 modifications were never the main focus of earth sciences, sometimes resulting in imprecise defini- larit etc. Dieser Beitrag ist eine überarbeitete und erweiterte Version eines im Jahr 2010 publizierten Klassifikationssys- tions of such raw materials. The most important SiO2 raw materials used in prehistory for the production of chipped tems für Gesteine der Chert-Gruppe. Das vorgeschlagene stone tools are silicites and thus part of the Chert Group, Bestimmungssystem basiert auf archäologischen, minera- such as chert, flint, radiolarite, etc. This paper is a revised logischen und geologischen Anforderungen und soll and extended version of a classification system for rocks Archäologen, die mit lithischen Materialien arbeiten, als within the Chert Group first published in 2010. The pro- handhabbares „research tool“ dienen. posed classification system is based on archaeological, min- eralogical and geological needs, and is intended to function Schlüsselwörter as a manageable research tool for archaeologists working Chert-Gruppe, Genese, Terminologie, Archäologie, Petro- with lithic materials. graphie, Mikropaläontologie, Klassifikationssystem. Keywords 1. Introduction Chert Group, genesis, terminology, archaeology, petrogra- Lithic provenance studies in an archaeological context phy, micropalaeontology, classification system. are mainly concerned with the identification of the pres- ence and consequently the use of local versus non-local raw Zusammenfassung materials (“exotic materials”). Research questions depen- Die Bestimmung des Rohmaterials prähistorischer Stein- dent on such provenance studies frequently examine inter- geräte stellt einen unerlässlichen analytischen Schritt zum actions between communities, transfer of knowledge and besseren Verständnis prähistorischen Ressourcenmanage- goods, early patterns of exchange and the exploitation and ments dar. Allerdings sehen sich Archäologen, die Rohma- use of certain raw materials for the production of “expedi- terialvarietäten lithischer Inventare bestimmen sollen, ent” or “formal” tools. Furthermore, the selection of raw einem terminologischen Dilemma gegenüber. Dies ist materials for the manufacture of stone tools often depends 34 Michael Brandl on raw material properties and can also be influenced by the determination of chert-varieties formed in genesis envi- certain preferences due to various reasons (e.g. sociocul- ronments related to the Tethys Ocean. The present paper tural and political). These considerations are fundamental represents the scientific foundation of the “2013 Classifica- attributes of prehistoric resource management. Diverging tion System for Single Artefact Recording”5 and is intended theoretical models that consider whether or not the raw to function as a research tool and communication catalyst material composition in lithic assemblages represents between geoscientists and archaeologists. meaningful human behaviour add to the complexity when studying mechanisms associated with prehistoric econo- 2. Setting the Frame: Definition of the Chert Group mies. Consequently, the initial step in studies based on Due to their natural abundance SiO2 rocks are of major lithic resource management is the accurate determination cultural importance since the beginning of stone tool man- of all raw materials contained in archaeological assem- ufacturing. With quartz as their dominating mineral com- blages, such as chert, flint, chalcedony, jasper, and others. ponent such rock varieties oftentimes only vary in their Nevertheless, lithic raw material determination from technical properties (e.g. texture, granularity, binding archaeological contexts is one of the most challenging agents, etc.). Partly overlapping terminology and the addi- archaeometric undertakings. This is especially true for SiO2 tional use of an abundance of regional and common names raw materials used for the production of chipped stone has significantly hampered the establishment of a clear ter- tools. These are predominantly rocks assigned to the Chert minology and classification of such rock varieties. 1 Group, generally referred to as “silicites”. Other than for Concerning the occurrence and variety of SiO2 rocks archaeologists, who are frequently forced to deal with such Götze states: “Silica (SiO2) makes up 12.6 weight% of the raw materials, silicites usually are of minor interest for geol- Earth’s crust as crystalline and amorphous silica in at least ogists and mineralogists due to their oftentimes monoto- 15 modifications […], i.e. mineral phases with the formula 6 nous composition, resulting in statements such as: “It is all SiO2 but a different crystal structure.” quartz anyway!” Thus, no international compulsive stan- Götze suggests a fundamental petrological classifica- dards for silicite nomenclature and classification have been tion of SiO2 rocks according to their magmatic, metamor- developed in geosciences, leaving archaeologists in a predic- phic or sedimentary origin.7 The majority of siliceous rocks ament. Therefore, it is understandable that researchers occur at the Earth`s surface, thus belonging to the group of started to create their own determination systems, which sedimentary rocks. The group of sedimentary SiO2 rocks lead to even greater confusion and exacerbating problems formed by chemical, biochemical and diagenetic SiO2 pre- concerning the comparability of data sets. The need for a cipitation can be best subsumed under the term “silicites” coherent classification system accepted by geoscientists and as proposed by several authors.8 manageable for archaeologists became urgent with the inten- Přichystal defines five basic groups for prehistorically sification of raw material sciences in archaeological research. used raw materials: (1) Siliceous sediments (silicites); (2) th The 2010 IMA-meeting in Budapest (20 General SiO2 minerals; (3) Natural glasses; (4) Clastic silica sedi- Meeting of the International Mineralogical Association ments; (5) Other rocks.9 “Bonds and Bridges: Mineral Sciences and their Applica- The present paper is focused on the first of these tions”) marked a changing point for terminological issues, defined groups, the siliceous sediments or silicites. Geneti- resulting in path-leading publications in the Archeometriai cally, silicites are non-detrital siliceous members within the Műhely-Series of the Hungarian National Museum.2 Some group of chemical sedimentary rocks, such as limestone. years have now passed and ongoing research in the course Members of the Chert Group, which form the central part of international projects has refined some of the initial of this contribution, constitute the most substantial com- 3 propositions formulated by the author. In addition to ponent within the sedimentary SiO2 rocks (or silicites). these new implications, enhanced background information According to Frondel, “chert, perhaps originally chirt, regarding the formation of chert and flint, geochemistry is believed to be a local English term that was taken into and alteration of silicite surfaces is provided here. The clas- geological use. It may be of onomatopoeic origin. The sification system proposed in the current paper is a refined name chert may be of more recent origin than flint, and version of the 2010 paper,4 which was chiefly designed for 5 Brandl et al. in press. 1 Přichystal 2010, 178. 6 Götze 2010, 164. 2 E.g. Biró 2010. – Götze 2010. – Přichystal 2010. 7 Götze 2010, 165. 3 Brandl 2010. 8 E.g. Götze 2010. – Přichystal 2010. − Přichystal 2013. 4 Brandl 2010. 9 Přichystal 2010, 178. Genesis, Provenance and Classification of Rocks within the Chert Group in Central Europe 35 unlike flint, is not found in literary usage. It was well estab- cambrian “iron-cherts” occur on the East European Plat- lished in meaning in 1679.”10 form, e.g. on the Baltic and Ukrainian shields.13 However, Petrographically, chert is a crypto- to microcrystalline those “chert” deposits were never used for the production rock mass, with SiO2 as the principal component. In pri- of chipped stone tools. mary deposition, it occurs in the form of nodules, concre- Palaeozoic cherts exist for example in the Barrandian, tionary masses or layers (tabular chert). When broken, in the Moravo-Silesian