Contents lists available at ScienceDirect Journal of Archaeological Science: Reports journal homepage: www.elsevier.com/locate/jasrep ‘Simple’ surface-fire heat treatment significantly improves silcrete flake quality and flaking efficiency Justin Pargeter a,b, ⁎ , Patrick Schmidt c,d a Department of Anthropology, New York University, NY, USA b Palaeo-Research Institute, University of Johannesburg, Johannesburg, South Africa c Eberhard Karls University of Tübingen, Department of Early Prehistory and Quaternary Ecology, Schloss Hohentübingen, 72070 Tübingen, Germany d Eberhard Karls University of Tübingen, Department of Geosciences, Applied Mineralogy, Wilhelmstraße 56, 72074 Tübingen, Germany ARTICLE INFO Keywords: Heat treatment Silcrete Raw material transformation Lithic miniaturization Experimental archaeology ABSTRACT Intentional stone heat treatment is a key marker for prehistoric behavioural variability. Yet, the relationship between differences in heat-treatment strategies and variations in stone tool-making processes remains heavily debated and poorly understood. We report on two experiments testing wood fuels and heating strategies applied to silcrete nodules from ~60 km south of Diepkloof Rock shelter in South Africa with early evidence for in- tentional silcrete heat treatment. We flaked the heated silcrete nodules to maximize miniaturized flake pro- duction. The resulting cores and flakes were compared in terms of their utility (flake cutting edge to mass) and cutting edge quality (cutting edge angles) in addition to quantifying woody residues and heat induced fracture rates. Our results show that ‘simpler’ surface-fire heat treatment strategies provide significant increases in miniaturized core utility and flake quality over unheated silcrete nodules. Some of these effects were obtained without more specialized knowledge than is required to maintain fires for cooking and other utilitarian purposes. Our results show that rapidly heating silcrete to modify rocks for miniaturized stone tool production is efficient at relatively low levels of technological investment. 1. Introduction Fire’s use to systematically manipulate the natural properties of rocks was a key Stone Age behavioral innovation. South Africa’s Middle Stone Age (MSA) record has in recent years attracted the attention of researchers partly because of its rich evidence for silcrete heat treat- ment (Schmidt et al., 2018; Domanski et al., 1994). Here prehistoric toolmakers used several heat treatment strategies across a region where silcrete is a relatively abundant rock type (Summerfield, 1981). These practices had great longevity, ranging from the second half of the MSA (~80 ka) into the Holocene (< 10 ka) (Delagnes et al., 2016; Porraz et al., 2016; Schmidt et al., 2015; Brown et al., 2009a). Archaeologists working in this region highlight heat treatment’s significance for our understanding of early human economic strategies (Brown and Marean, 2010) and technological innovations (Sealy, 2009). Recent progress has been made on the methods to recognize heat treatment (Schmidt et al., 2017a), to understand the thermal processes that take place (Schmidt et al., 2018; Schmidt et al., 2017a; Schmidt et al., 2013), and to esti- mate the time and energy costs involved (Schmidt et al., 2015; Schmidt et al., 2013; Stolarczyk and Schmidt, 2018). One major outstanding question regards early silcrete heat treat- ment’s cognitive implications. Schmidt et al. (2013) propose that the invention of temperature induced transformations of silcrete did not require the setup of a dedicated heating environment using sand baths and may have been performed in the same contexts as other fire related activities. If these observations are correct, then rapidly heated silcrete to modify rocks for stone tool production would be efficient at rela- tively lower levels of investment in skill learning than otherwise thought (Wadley and Prinsloo, 2014a; Brown et al., 2009b). And in- deed, sand-bath heating has been described as requiring higher in- vestment in terms of resources and cognition (see for example: Brown and Marean, 2010; Wadley and Prinsloo, 2014b) and as being techno- logically more complex than open-air fire-based heating techniques (Stolarczyk and Schmidt, 2018). Given the early dates for heated sil- crete in southern Africa, a potential finding that heat treatment with 'simpler' surface-fire techniques is more effective would support the hypothesis that humans made key and early innovations in raw mate- rial preparation strategies but that the time and energy investments required are less than currently thought. This study examined several hypotheses regarding the technological https://doi.org/10.1016/j.jasrep.2020.102203 Received 12 August 2019; Received in revised form 9 December 2019; Accepted 9 January 2020 ⁎ Corresponding author at: Department of Anthropology, New York University, NY, USA. E-mail address: justin.pargeter@nyu.edu (J. Pargeter). Journal of Archaeological Science: Reports 30 (2020) 102203 2352-409X/ © 2020 Elsevier Ltd. All rights reserved. T