Coal is a multicomponent rock formed from the products of biochemical and physicochemical transformation of plant matter. The changes of coal organic matter under various geological conditions of formation are responsible for the existence in nature of their numerous types and varieties.The structural-textural features of coals are formed at all stages of the development of coal-bearing basins, beginning with the peat stage of coal formation. According to the macrostructure in coal seams bundles are distinguished composed of homogeneous (rather seldom) and inhomogeneous (as a rule) coal. Homogeneous coals do not contain inclusions visible to the naked eye. In contrast, inhomogeneous coals are characterized by inclusions of less decomposed plant remnants, usually in the form of vitrain and fusain. These inclusions are evident at coal fractures oriented perpendicular to the lamination, in the form of lenses and bands of brilliant shiny and fibrous opaque coal, respectively. They are also visible on coal surfaces oriented by layers since in a number of cases they are the weakest regions in the coal seam.
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