Cell dimensions, minor element composition and high-low inversion of quartz in the Amakusa pottery stone.

Abstract

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 A and c=5.4047–5.4057 A 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.