Quartz is the predominant constituent of the Amakusa pottery stone together with sericite and kaolin minerals. The quartz grains are 10–60 μm in size and show undulatory extinction under the microscope. X-ray diffraction, electron microprobe, and differential thermal analyses have revealed the following properties of the quartz.
X-ray diffraction peaks of the quartz are broad. The cell dimensions are relatively large with a=4.9137–4.9155 Å and c=5.4047–5.4057 Å at 21°C. Most quartz samples show relatively high Al₂O₃ contents around 0.1 up to 1 wt% in maximum, and are inhomogeneous in the Al₂O₃ content among quartz grains. The high-low inversion peak in the DTA curve is broad and the peak temperature is by 2–12°C lower than that of ordinary quartz.
Thus the quartz in the Amakusa pottery stone is characterized by the large cell dimensions, the high Al content, the low temperature of the high-low inversion, the relatively low crystallinity and some inhomogeneity.

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The possibility of annealing of radiation damage in minerals and hence of track fading, always exists. This effect can be in response to a short time, higher temperature event, or be caused by prolonged annealing, at only a slightly elevated temperature during the geothermal history of earths crust. Track retention in minerals apatite, chlorite, biotite, phlogopite, muscovite, garnet, epidote and zircon have track retention over a wide range of temperatures (90–250°C), when we consider closing temperatures for fission track system. Further experiments have been made to determine the calibration curves relating track length shrinkage with track density reduction.

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Thirty three years ago, the present author described the high-temperature optics of natural sodic plagioclases in Miocene rhyolites from northern Japan. In this paper, the same specimens of sodic plagioclases are carefully reexamined with aids of EPMA to check and revise the author’s previous diagrams. Point-by-point chemical analyses followed by the measurement of extinction angles are practiced on some zoned plagioclases perpendicular to a-axis (PM). The results show that the optical data are still useful.

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