MIKASAITE, (FE3+, AL)(2)(SO4)(3), A NEW FERRIC SULFATE MINERAL FROM MIKASA CITY, HOKKAIDO, JAPAN

The new ferric sulphate mineral, mikasaite, the Fe analogue of millose vichite was found in Ikushunbe tsu, Mikasa city, Hokkaido, Japan. Mika saite occurs as a sublimate around fractures from which coal gas escap es. The white-light brown coloured mineral shows aggregates of fine po rous crystals. The SEM micrographs indicate that the aggregates are ho llow spherical crystals of 100 mu m average diameter and 1-5 mu m thic kness. Microprobe analysis, SO3 by wet analysis and H2O by moisture ev olution 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 H 2O on its surface because of its strong deliquescence. As H2O is not e ssential to the mikasaite structure, the empirical formula on the basi s of 3SO(4) is (Fe1.56Al0.44Mn0.03)(Sigma 2.03)(SO4)(3.00), ideally Fe -2(SO4)3. The strongest 10 lines in the X-ray powder diffraction patte rns, indexed on a hexagonal unit cell are (d,I/I-o,hkl): 3.56, 100, 11 3; 5.99, 28, 012; 4.35, 23, 104; 2.97, 20, 024; 2.72, 20, 116; 2.64, 1 1, 211; 2.35, 7, 300; 2.24, 6, 303; 1.78, 6, 226; 3.68, 5, 006. It has space group R (3) over bar with hexagonal lattice parameters of a=8.1 4(1) and c=21.99(8) Angstrom.