Magnetic property-based provenance investigation of Hokkaido (Japan) archaeological obsidian tools

The obsidian obtained from Shirataki, Japan, was analyzed with a Mössbauer spectrometer. The Mössbauer spectra at 295 K were characterized by two sextets (magnetite-tet/oct sites), two ferrous iron doublets (olivine and pyroxene), and a ferric iron doublet (tentatively associated to the nano-oxide phase). The main phases of the Hokkaido obsidians are olivine, pyroxene, magnetite, and nano-oxide. The biotite found in Kyushu obsidian was absent in the Hokkaido obsidian. Instead, the Hokkaido obsidian consisted of nano-iron oxide. In obsidians, iron species are mostly hosted by divalent ions of olivine and pyroxene. Some Hokkaido obsidian showed the presence of hematite. The distribution and presence of these iron species indicates that they were formed differently from the environments of Kyushu, Japan. This study further entailed a comparison of the magnetic behavior of the archaeological and geological obsidian by examining the magnetic parameters based on the Mössbauer spectroscopy, thus demonstrating its applicability in obsidian sourcing research.