John S McCloy1,2,3,4, José Marcial5,6, Jack S Clarke7, Mostafa Ahmadzadeh5,8, John A Wolff9, Edward P Vicenzi10, David L Bollinger8, Erik Ogenhall11, Mia Englund11, Carolyn I Pearce6, Rolf Sjöblom12, Albert A Kruger13. 1. School of Mechanical and Materials Engineering, Washington State University, Pullman, WA, USA. john.mccloy@wsu.edu. 2. Materials Science and Engineering Program, Washington State University, Pullman, WA, USA. john.mccloy@wsu.edu. 3. Department of Materials Science and Engineering, University of Sheffield, Sheffield, UK. john.mccloy@wsu.edu. 4. Pacific Northwest National Laboratory, Richland, WA, USA. john.mccloy@wsu.edu. 5. School of Mechanical and Materials Engineering, Washington State University, Pullman, WA, USA. 6. Pacific Northwest National Laboratory, Richland, WA, USA. 7. Department of Materials Science and Engineering, University of Sheffield, Sheffield, UK. 8. Materials Science and Engineering Program, Washington State University, Pullman, WA, USA. 9. School of the Environment, Washington State University, Pullman, WA, USA. 10. Museum Conservation Institute, Smithsonian Institution, Suitland, MD, USA. 11. The Archaeologists, National Historical Museums (SHM), Uppsala, Sweden. 12. Luleå University of Technology, Luleå, Sweden. 13. US Department of Energy, Richland, WA, USA.
Abstract
European Bronze and Iron Age vitrified hillforts have been known since the 1700s, but archaeological interpretations regarding their function and use are still debated. We carried out a series of experiments to constrain conditions that led to the vitrification of the inner wall rocks in the hillfort at Broborg, Sweden. Potential source rocks were collected locally and heat treated in the laboratory, varying maximum temperature, cooling rate, and starting particle size. Crystalline and amorphous phases were quantified using X-ray diffraction both in situ, during heating and cooling, and ex situ, after heating and quenching. Textures, phases, and glass compositions obtained were compared with those for rock samples from the vitrified part of the wall, as well as with equilibrium crystallization calculations. 'Dark glass' and its associated minerals formed from amphibolite or dolerite rocks melted at 1000-1200 °C under reducing atmosphere then slow cooled. 'Clear glass' formed from non-equilibrium partial melting of feldspar in granitoid rocks. This study aids archaeological forensic investigation of vitrified hillforts and interpretation of source rock material by mapping mineralogical changes and glass production under various heating conditions.
European Bronze and Ironpan class="Gene">Age vitrified hillforts have been known since the 1700s, but archaeological interpretations regarding their function and use are still debated. We carried out a series of experiments to constrain conditions that led to the vitrification of the inner wall rocks in the hillfort at Broborg, Sweden. Potential source rocks were collected locally and heat treated in the laboratory, varying maximum temperature, cooling rate, and starting particle size. Crystalline and amorphous phases were quantified using X-ray diffraction both in situ, during heating and cooling, and ex situ, after heating and quenching. Textures, phases, and glass compositions obtained were compared with those for rock samples from the vitrified part of the wall, as well as with equilibrium crystallization calculations. 'Dark glass' and its associated minerals formed from amphibolite or dolerite rocks melted at 1000-1200 °C under reducing atmosphere then slow cooled. 'Clear glass' formed from non-equilibrium partial melting of feldspar in granitoid rocks. This study aids archaeological forensic investigation of vitrified hillforts and interpretation of source rock material by mapping mineralogical changes and glass production under various heating conditions.
Authors: Fabian B Wadsworth; Michael J Heap; David E Damby; Kai-Uwe Hess; Jens Najorka; Jérémie Vasseur; Dominik Fahrner; Donald B Dingwell Journal: Sci Rep Date: 2017-01-12 Impact factor: 4.379