DETECTING AND QUANTIFYING HEAT TREATMENT OF FLINT AND OTHER SILICA ROCKS: A NEW NON‐DESTRUCTIVE METHOD APPLIED TO HEAT‐TREATED FLINT FROM THE NEOLITHIC CHASSEY CULTURE, SOUTHERN FRANCE

Heat treatment of lithic raw material is known from the Middle Stone Age to the Neolithic. These findings require archaeometric techniques and methods for detecting the heat-induced effects within lithic artefacts. However, the existing methods are often cost-intensive and time-consuming, and most of them are destructive. Here, we present a new method using the infrared spectroscopic measurement of the strength of H-bonds formed between surface silanole groups (SiOH) and H2O molecules held in open pores of the samples. The reduction of H-bond strength in chalcedony is shown to be strongly correlated with the loss of open pores induced by heat treatment. Hence, the method is based on measuring one of the transformations aimed for by the instigators of the heat treatment: the reduction of porosity that modifies the rock's mechanical properties. A first application to heat-treated material from the Neolithic Chassey culture (southern France) shows that flint was heated to temperatures between 200°C and 250°C in this period. This has important implications for the study of the procedures used and the heating environments. Our new method is non-destructive, rapid, cost-effective and allows for detection of the used annealing temperatures.

[1]  M. Symons,et al.  Identification of ancient heat treatment in flint artefacts by ESR spectroscopy , 1978, Nature.

[2]  F. Bordes.  Traitement thermique du silex au Solutréen , 1969 .

[3]  C. Melcher,et al.  Thermoluminescent Determination of Prehistoric Heat Treatment of Chert Artifacts , 1977, Science.

[4]  P. Sheppard,et al.  Thermoluminescent Determination of Paleoindian Heat Treatment in Ontario, Canada , 1983, American Antiquity.

[5]  J. White,et al.  Detecting Heat Treatment on Silcrete: Experiments with Methods , 1997 .

[6]  L. Larsson,et al.  Testing for the Presence of Thermal Pretreatment of Flint in the Mesolithic and Neolithic of Sweden , 1982 .

[7]  V. Léa.  Centres de production et diffusion des silex bédouliens au chasséen , 2004 .

[8]  G. Rossman,et al.  Hydrogen speciation in synthetic quartz , 1984 .

[9]  S. Nakashima,et al.  Water at high temperatures in a microcrystalline silica (chalcedony) by in-situ infrared spectroscopy : physicochemical states and dehydration behavior , 2008 .

[10]  A. Kronenberg.  Hydrogen speciation and chemical weakening of quartz , 1994 .

[11]  A. Kronenberg.  Chapter 4. HYDROGEN SPECIATION AND CHEMICAL WEAKENING OF QUARTZ , 1994 .

[12]  M. Lévy,et al.  Mémoire sur les diverses formes affectées par le réseau élémentaire du quartz , 1892 .

[13]  P. Villa,et al.  Early Use of Pressure Flaking on Lithic Artifacts at Blombos Cave, South Africa , 2010, Science.

[14]  H. Chandra,et al.  Trapped methyl radicals in chert , 1982, Nature.

[15]  R. Butler,et al.  Notes on experiments in flint knapping. 1. Heat treatment of silica materials , 1964 .

[16]  P. Vermeersch,et al.  A Middle Paleolithic site with blade technology at Al Tiwayrat, Qena, Upper Egypt , 2005 .

[17]  G. Miehe,et al.  The nature of water in chalcedony and opal-C from brazilian agate geodes , 1985 .

[18]  E. Salje,et al.  Nanoquartz vs. macroquartz: a study of the α↔β phase transition , 2001 .

[19]  Zenobia Jacobs,et al.  Fire As an Engineering Tool of Early Modern Humans , 2009, Science.

[20]  G. Borradaile,et al.  Magnetic and Optical Methods for Detecting the Heat Treatment of Chert , 1993 .

[21]  Patrick Schmidt,et al.  Crystallographic and structural transformations of sedimentary chalcedony in flint upon heat treatment , 2012 .

[22]  F. Fröhlich,et al.  Detailed FT near-infrared study of the behaviour of water and hydroxyl in sedimentary length-fast chalcedony, SiO2, upon heat treatment. , 2011, Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy.

[23]  M. Symons,et al.  MANGANESE (II) AS AN INDICATOR OF ANCIENT HEAT TREATMENT IN FLINT , 1981 .

[24]  V. Lea.  Raw, pre-heated or ready to use: discovering specialist supply systems for flint industries in mid-Neolithic (Chassey culture) communities in southern France , 2005, Antiquity.

[25]  H. Irwin,et al.  Age Determination of Burned Flint by a Thermoluminescent Method , 1974, Science.

[26]  O. W. Flörke,et al.  Water in microcrystalline quartz of volcanic origin: Agates , 1982 .