Due to dynamic climatic changes resulting, among others, from the use of coal, the content of harmful substances in coal is of particular importance. Dangerous air pollution resulting from the burning of coal (e.g. As, Se, Hg, Pb, Sb) is often associated with sulfide minerals in coal. The study focused on the sulphides occurring in Polish hard coal deposits. Sulfides are one of the forms of occurrence of sulfur in coal. In this paper, an emphasis has been placed on on the characteristics of forms of occurrence of sulphides on both macroscopic and microscopic scale and on the chemical analysis in the micro area. The study has been conducted for the No. 301–308 seams from the eastern part of the Upper Silesian Coal Basin, stratigraphically belonging to the highest part of the Orzesze Beds s.s. (Westphalian B). The coal samples have been collected from the coal seams in the underground excavations of the following coal mines: Jan Kanty, Sobieski Jaworzno I, Wesoła and Ziemowit hard coal mine.
Iron sulfides (pyrite, marcasite) in coal seams of the Orzesze Beds s.s. form various forms of macroscopically visible aggregates. These include massive, vein, pocket-like (impregnation) or dispersed forms. On the basis of microscopic observations, the following forms of occurence of iron sulphides in the tested coal have been determined: skeletal and massive vein forms, massive pocket-like (impregnation) forms, framboidal pyrite and euhedral crystals. The most common form of sulfides in the studied coal seams are vein forms cutting across bedding, usually creating complex dendritic and skeletal forms. Iron sulfides often occur in pocket-like (impregnation) forms, not directly linked with vein forms and fusinite. The WDS analysis in the micro area has revealed the chemical composition of sulfides in eight coal samples. As follows from the analysis, the tested coal seams are dominated by FeS2 iron sulfides. It has been shown that the iron sulfides contained small admixtures of Pb, Hg, Zn, Cu, Ag, Co Sb and Ni. The admixtures of As and Cd have been observed only in individual minerals. Lead, reaching up to 1.06%, has the highest concentration out of all admixtures in pyrite and marcasite. Small amounts of galena, titanium oxides (rutile), monazite and barite have also been found in the tested coal samples. Locally, vein forms, pyrite and dolomite were interlaying each other; the same applies to pyrite and apatite. In addition, dolomite fills part of the cells in fusinite.