New Britain obsidian sources

The natural occurrence of obsidian in volcanic flows in West New Britain has been thoroughly investigated and new measurements of the composition of field samples have been made with a proton dose of 150 μC, increased by a factor of three compared to analyses reported in early studies. New data on precision and accuracy of PIXE-PIGME show that measurement error is not a significant factor in interpretations of chemical variability among source and artifact samples. The results provide evidence for 5 readily distinguishable groups of source samples (Gulu, Kutau/Bao, Baki, Hamilton and Mopir) plus two subgroups (GaralaB and GaralaC) which differ from the Baki source for a few elements and have higher standard deviations from most elements. An unusual degree of variability within the Hamilton and Garala source samples must be taken into account during the classification of artifact collections.