多賀城跡古代瓦の鉱物学的研究

抄録

An old castle named Tagajo was founded between the 8th and 11th Centuries in Miyage Prefecture, Japan. Roofing tiles were unearthed from the ruins of castle and old oven, which were studied by mineralogical methods.
Roofing tiles used in the study were classified from archaeology into two groups, one of which was the I era tiles and the other the II, III and IV era tiles. Every tiles were 12 to 34mm in thickness. The I tiles were homogeneous with light dark color and the others inhomogeneous roughly with ashy color. In every tiles many porphyritic quartz crystals were found in association with plagioclase, hornblende, augite and magnetite under a microscope. Their groundmasses consisted of quartz and glassy materials.
Textures were found to be fluidal, banded and microfolded in the I tiles, and were more notable than those of the II to IV tiles. From X-ray diffraction patterns the presence of quartz, plagioclase, cristobalite and mullite was detected. From chemical analyses all compositions concentrated on a small area centered at 70% SiO₂, 20% Al203 and 10% the others in the triangle phase diagram. Refractorinesses of every tiles were found to be under SK 26. Water absorptions of these tiles satisfies a requirement of the JIS standard for roofing tiles.
From these results it was found that the fired temperatures were between 1, 000° and 1, 200°C and the techniques making roofing tiles progressed from the I era to the II to IV eras.