M. Járó - L. Költő szerk.: Archaeometrical research in Hungary (Budapest, 1988)

Analysis - BIRÓ Katalin, POZSGAI Imre, VLADÁR András: Central European obsidian studies. State of affain in 1987

BIRÓ Katalin*, POZSGAIImre**, VLADÂR András** CENTRAL EUROPEAN OBSIDIAN STUDIES. STATE OF AFFAIRS IN 1987 Abstract - 777« paper contains a brief summary of the data on Central European obsidian, comprising archaeological and geological evidence as well as results of archaeometrical investigation. Recent results of obsidian analyses by electron energy dispersive X-ray spectrometry are demonstrated, and research tasks proposed for the near future. Introduction Obsidian research is one of the favourite, we may even say classical fields of archaeometrical investigations. The reason for it lies in the manifold favourable qualities offered by obsidian in investigating the past. Obsidian is a natural glass of volcanic origin. It is a rock formed of acidic (high silica content) magma, as a result of very quick cooling, ''quenching". Therefore its chemical composition is characteristic of a given area, better to say, a given magmatic chamber. The chemical composition varies, in accordance with the narrow optimum range of glass formation, to a relatively small extent among the main components for all sources, but the different sources give obsidian varieties separable from each other because the homogeneity within one source is normally very high and the differences among the different sources are detectable with good precision and accuracy. Differences in the trace element content of obsidians coming from different sources exceed variations of the main component. Apart from the characteristic chemical composition, the amorphous structure as well as the instantaneous quenching of obsidian offers further chances for archaeometrical investigation. The natural glass contains varying amount Of radioactive materials, among them uranium, the natural decay of which is the basis of fission track dating (FTD). FTD can be very useful for source characterization, and in the quite frequent instances when obsidian suffered the effect of heating in an archaeological context, it can be used for dating the archaeological assemblage as well. The natural glasses are not stable under normal surface pressure and temperature conditions; the amorphous rocks composed of multi-oxide silicate melt undergo a timeand heat-dependent process of crystallization in the presence of vapour. This process starts from the surface (or fissures) of the object proceeding inwards; this phenomenon is the basis of obsidian hydration dating (OHD). At the same time, we must not forget about the potentials of more or less traditional morphological and technological investigation to which all hthic implements can be subjected [1—3]. In the following, we shall try to give a brief sketch on obsidian studies relevant to the Hungarian material, and also give an account of some recent developments that have not, as yet, been published. * Archaeological Institute H-1250 Budapest, Uri u. 49. * Institute of Technical Physics H-1047 Budapest, Fóti u. 56.