Igneothermally Altered Coal of Lish-Ramthi Valley, Darjeeling District

Chemical analysis of the coke shows that volatile matter and moisture content increase away from the igneous contact. Resistivity measurement of the samples shows that the resistivity of the natural coke increases away from the igneous contact. Microscopic constituents according to the properties under reflected polarized light can be divided into three groups: (i) Mosaic unit; (ii) Macerals with cell structure and (iii) Homogeneous mass without cell structure. Mosaic units are altered products of reactive vitrinite. 'Sphere' of both larger and smaller dimensions are present in the altered mass of the natural coke. Inert vitrinites are high reflecting masses without bireflectance and anisotropism. Macerals with cell structures present are the fusinite and semifusinite in the coal. Some lamellar masses present in the coal are strongly anisotropic and bireflecting. Under crossed nicols they get divided into several ribbon like masses with alternate light and dark bands.