Tsutomu Nishiyama

An Interstratified Chlorite-Vermiculite in Weathered Red Shale Near Toyoma, Japan

Abstract An interstratified chlorite-vermiculite altered from chlorite by weathering is found in the weathered red shale near Toyoma in Miyagi Pref., Japan. This mineral shows a very strong reflection at 14.7a with an almost regular series of basal reflections, but does not show a reflection with a long spacing. The characteristic behaviour of the basal reflections after various treatments shows clearly the presence of chlorite and vermiculite layers in this mineral. The ratio of chlorite layer and vermiculite layer is 1:1 in the mineral. The structure of this mineral deviates from a 1:1 regular interstratification of chlorite and vermiculite layers, but is not a completely random one. Dehydration of the vermiculite layer occurs mainly at about 56-83°C and 159°C, and dehydration of the hydroxyl sheet in the chlorite layer occurs at about 555°C. The chemical formula obtained for the mineral is 11.2SiO 2 4.2A1 2 O 3 8.7MgO 3.OFe 2 O 3 10.6H 2 O. Cation exchange capacity is estimated to be 60meq/100g and the calculated interlayer charge of vermiculite layer is 1.01 on the basis of a O 2o (OH) 4 unit.

X-ray basal reflection intensities and chemical compositions of dioctahedral mica clay minerals

The intensities of X-ray basal reflections of dioctahedral mica clay minerals were calculated on the basis of the mica compositions ranging from K2 (Al, Si)8 Al4O20(OH)4 to (K, H2O)2-0 (Al, Si)8 (Al2Fe2) O20 (OH)4. The triangular diagrams with three components, I(10A)-I(5A)-I(3.3A) and I(5A)-I(3.3A)-I(2.5A), were made from these intensities calculated. Figures showing relationship between I(10A)/I(5A) or I(10A)/I(3.3A) and the contents of interlayer or octahedral cations were also made. Basal reflection intensities were examined for some illite samples having different chemical compositions. These samples were plotted in the above-mentioned diagrams and figures. Relationship between the points of samples in the figures and their compositions were investigated. Some problems were pointed out for the practical method obtaining chemical compositions of dioctahedral mica clay minerals from the ratios of basal reflection intensities.