The constituent minerals of the ores of the Amakusa pottery stone deposits have been examined by X-ray powder method, electron probe microanalysis, differential thermal analysis, polarizing microscopy, etc. The main constituent minerals of the pottery stones are quartz, sericites and kaolinite. Minor components of them are dickite, rectorite, tosudite, smectite, plagioclase, K-feldspar, calcite, siderite, pyrite, etc., among which the first three minerals occur only in the Sarayama vein. Feldspar, carbonate and pyrite are more abundant in the Kaigan and Murayama veins.
X-ray diffraction peaks of the quartz are broard. The cell dimensions are relatively large with α=4.9137-4.9154 Å and
c=5.4047-5.4057 Å at 21°C. Most quartz samples show relatively high Al
2O
3 contents around 0.1wt% up to 1wt% in maximum, and are inhomogeneous in the Al
2O
3 content among grains. The high-low inversion peak in the DTA curve is broad and the peak temperature is lower than that of common quartz.
Sericites in the ores of the Sarayama vein comprises coarse-grained 2
M1 and 1
M micas and finegrained irregularly interstratified 1
M mica/smectite with small amounts of smectite layers. Sericites in the ores of the Kaigan and Murayama veins are mostly coarse-grained 2
M1 and 1
M micas. These coarse-grained micas often form banded structure in which 2
M1 mica tends to grow inside. Tetrahedral and interlayer compositions of the 2
M1 mica are close to those of ideal muscovite although octahedral Fe and interlayer Na are appreciably contained. The 1
M mica and fine-grained irregularly interstratified 1
M mica/smectite have less tetrahedral Al and interlayer cations, and the contents of octahedral Fe and interlayer Na are very small. Such a difference in chemical composition between 2
M1 and 1
M micas is most pronounced in those of the Sarayama ores. The observed variations of sericites in chemical composition, polytype and interstratification are discussed with their genesis.
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