Mikasaite, (Fe3+, Al)2(SO4)3, a new ferric sulphate mineral from Mikasa city, Hokkaido, Japan

Abstract

AbstractThe new ferric sulphate mineral, mikasaite, the Fe analogue of millosevichite was found in Ikushunbe tsu, Mikasa city, Hokkaido, Japan. Mikasaite occurs as a sublimate around fractures from which coal gas escapes. The white-light brown coloured mineral shows aggregates of fine porous crystals. The SEM micrographs indicate that the aggregates are hollow spherical crystals of 100 µm average diameter and 1–5 µm thickness. Microprobe analysis, SO3 by wet analysis and H2O by moisture evolution analyser gives Fe2O3 24.3, Al2O3 4.3, Mn2O3 0.5, SO3 46.8, H2O(−) 23.0, total = 98.9 wt.%. The specimen adsorbed a large amount of H2O on its surface because of its strong deliquescence. As H2O is not essential to the mikasaite structure, the empirical formula on the basis of 3SO4 is (Fe1.56Al0.44Mn0.03)Σ2.03(SO4)3.00, ideally Fe2(SO4)3. The strongest 10 lines in the X-ray powder diffraction patterns, indexed on a hexagonal unit cell are (d,I/Io,hkl): 3.56, 100, 113; 5.99, 28, 012; 4.35, 23, 104; 2.97, 20, 024; 2.72, 20, 116; 2.64, 11, 211; 2.35, 7, 300; 2.24, 6, 303; 1.78, 6, 226; 3.68, 5, 006. It has space group R with hexagonal lattice parameters of a= 8.14(1) and c = 21.99(8) Å.