Context:

The geochemical characterization of archeological materials of obsidian or volcanic glass (used in the past for the preparation of lithic tools) allows to trace origin and infer forms of interaction and ranges of mobility of ancient human populations. The characterization of the geochemical composition of obsidian by analysis of Neutron Activation allows to determine with a good degree of certainty its origin; however, it is a costly and destructive technique, not recommended for archeological pieces. Other more accessible techniques, such as X Ray Fluorescence or Mass Spectrometry with inductively coupled plasma have been used successfully for this application but with a higher level of uncertainty. This work seeks to provide solutions through the use other non-destructive techniques that may be applicable to archeological heritage.

Method:

The mechanical properties of an obsidian sample were explored through ultrasound methods. The phase velocity and the attenuation of longitudinal waves were measured, and the density of the samples was quantified with gas pycnometry, which makes it possible to determine the dynamic elastic modules. Additionally, the same measurements were repeated on glass samples of industrial manufacture.

Results:

It was observed that the speed, density, and longitudinal modulus were higher for the industrial glass sample than for the obsidian sample. Conversely, the attenuation was greater in the case of obsidian, and a greater dependence on frequency was observed.

Conclusions:

The results obtained demonstrate the ability of the method to distinguish between materials with different chemical composition; thus, it would be useful in archeological studies. Moreover, the differences observed in the attenuation show that the method is sensitive to the microstructure of the material, so it would provide information not accessible by conventional archaeometry techniques.