山口県における石器原材の原産地推定 岩石学的手法による解明の例

Abstract

Sanukitic andesite, glassy andesite and obsidian are found from six sites, including Kozaki, Fujio-yama, Iwagami, Nagamasu, Minamikata and Amagoidai sites, in Yamaguchi prefecture; they range in age from palaeolithic to Jomon period. These volcanic rocks are carried from a distance. The authors undertook speculative research to determine the original localities of these rocks using three petrological methods: megascopic judgement, polarized microscopic judgement, and comparison of main chemical compositions by X-ray fluorescence analysis.With megascopic judgement, it was possible to identify the source of rocks only in some special cases. Examples are the greyish white obsidian from Kannon-zaki, Hime-shima island, Oita prefecture. This obsidian was found at six sites.Polarized microscopic judgement is an effective measure for the andesitic rocks.With its use, we identified sanukitic andesite from Hari-yama, Hiroshima prefecture, in five of the six sites (all except Amagoidai), another sanukitic andesite from Taku, Saga prefecture, in the Fujio-yama and Minamikata sites, and glassy andesite from Himeshima island, Oita prefecture, in all six sites.X-ray fluorescence analysis is a convenient method for identifying black obsidian. It enabled us to identify obsidian from Kumi, Oki-Dogo island, Shimane prefecture, in the Kozaki and Fujio-yama sites, another obsidian from Matsuura, Nagasaki prefecture, in the Iwagami site, and an obsidian from Koshi-dake, Saga prefecture, in all six sites.