B. Kwiecińska

On the optically biaxial character and heterogeneity of anthracites

Abstract The results of the study of optical properties of 13 anthracites from different parts of the world are presented in this paper. Measurements of reflectance values were made on non-oriented vitrinite grains for a minimum of 300 points per sample. The reconstruction of Reflectance Indicating Surfaces (RIS) were made by Kilbys method [Kilby, W.E., 1988. Recognition of vitrinite with non-uniaxial negative reflectance characteristics. Int. J. Coal Geol. 9, 267–285; Kilby, W.E., 1991. Vitrinite reflectance measurement — some technique enhancements and relationships. Int. J. Coal Geol. 19, 201–218]. It was found that the use of Kilbys method for strongly anisotropic materials like anthracites did not give unambiguous results. Some improvement in Kilbys method, consisting of the division of the cumulative cross-plot into several elemental components, is suggested. Each elemental cross-plot corresponds to a textural class of anthracite, which is characterized by the values of RIS main axes RMAX(k), RINT(k) and RMIN(k) (k=1,2,…n; n — number of classes). The global texture of anthracite is characterized as a RIS with main axes calculated as the weighted means of R MAX , R INT and R MIN for each class of this anthracite. The division of cumulative Kilbys cross-plot on elemental components makes possible the calculation of new coefficients Ht and H10 characterizing the heterogeneity of the structure and texture of anthracites. The results of our study show that all anthracites have biaxial negative textures, but their heterogeneity varies in a wide range of Ht and H10 coefficients depending upon the individual coal basin.

Textural transformation of thermally treated anthracites

Abstract The organic matter of anthracites consists of turbostratic (two-dimensional crystalline order) stacks of three to five aromatic layers called the Basic Structural Units (BSU). The arrangement of BSU forms the texture of anthracites, which corresponds to their chemical and physical properties including optical properties (reflectance values). Thermal treatment leads to the changes in the arrangement of BSU. The character of structural and textural transformation of anthracites during heating can be determined based on the changes of reflectance values of anthracites. Several anthracites of various ranks were thermally treated over the temperature range of 400 (673 K)–1000 °C (1273 K) in an inert atmosphere (N2), at atmospheric pressure. The reflectance indicating surfaces (RIS) were reconstructed and reflectance indicatrix parameters were calculated according to the Kilby method specially modified for the study of anthracites. It was found that the relative increase of reflectance values (Rmax, Rmin) was greater for the lower metamorphosed samples than for the higher ones. However, the higher rank of initial samples, the greater their final reflectance values and the anisotropy of the texture attained at 1000 °C. It indicates that the texture of the higher metamorphosed anthracites (meta-anthracites) is more flexible for rearrangement during heating, than the texture of the lower metamorphosed anthracites. Moreover, the difference in the changes of reflectance values versus temperature for the higher and for the lower rank anthracites suggests that meta-anthracites have undergone stronger natural metamorphism equivalent to about 200 °C in comparison with the other anthracites. It could be said that the character of textural transformations of individual anthracites results from the degree of their metamorphism and, in a consequence, from the texture of parent sediments.

Facies analysis of coal seams from the Cracow Sandstone Series of the Upper Silesia Coal Basin, Poland

Abstract The main purpose of this study was to recognise the variability of petrographical structure of two coal seams occurring in the Cracow Sandstone Series (Upper Carboniferous/Pennsylvanian, Upper Westphalian), being exploited in the Siersza mine. This mine is located in the eastern part of the Upper Silesia Coal Basin (USCB). The chemical analyses and petrographical features allow the inclusion of these coals to the group of hard brown coals belonging to subbituminous class. Two coal seams (207 and 209/210) of a considerable thickness (7.44 and 6.54 m, respectively), representative of the Cracow Sandstone Series (CSS), were chosen for the petrographic studies. Dominant macroscopic constituents of both seams are banded bright coal and banded coal. The coal seams were sampled in 284 intervals using a channel profile sampling strategy. The microscopical examinations revealed the majority of macerals from the vitrinite group (55%), followed by inertinite (21%), liptinite (11%), and mineral matter (13%). Low values of the vitrinite reflectance ( R o =0.46%) confirm very low coalification of the coal in both seams. Facies analysis indicates that in the course of a mire development, in which the studied coal seams originated, wet forest swamp conditions dominated characterized by a high degree of flooding and gelification as well as by a prevalence of arborescent plants. In such conditions, lithotypes with a large content of bright coal were mainly formed. Petrographic and facies data point to the rheotrophic character of these peatbogs. Frequent changes of the conditions in the peatbog, as it is shown by the variability of petrographic structure of the studied profiles, as well as by lateral changes of the phytogenic sedimentary environment within the coal seams, indicate a strong influence of a river channel on the adjoining peatbogs. An accretion of clastic sediments within the wide river channel belts was balanced mainly by the peatbog growth on the areas outside channels. Frequency and rate of avulsion of the river channels influenced the size, continuity and variability of the peatbogs.

The study of textural and structural transformations of carbonized anthracites

Abstract Specific physical and chemical properties of anthracites may be explained by the differences in chemical structure of basic structural units (BSUs) and in various spatial arrangements of BSUs, that is, the texture. The structure and the texture of anthracites correspond with their optical properties. Thermal treatment causes the changes in the structure of BSUs and rearrangement of the texture of anthracites. The character of structural and textural transformation could be determined based on the reflectance values of anthracites. Various anthracites were thermally treated to the temperature of 1800 °C. Maximum ( R max ) and minimum ( R min ) reflectance values were measured and reflectance indicatrix parameters ( R ev , R st and R am ) were calculated for initial and heated samples. It was found that R max , R min and R ev values increase together with the temperature up to 1200–1400 °C. In higher temperatures, they start to decrease, while R am parameter depending on anisotropy of the texture still increases to the final temperature of 1800 °C. That indicates gradual and soft transformation of the structure and the texture of anthracites up to the temperature 1200–1400 °C (arrangement of turbostratic structure) and some disturbances in textural order before the stage of graphitization.

Geochemical studies of natural graphites by INAA determined trace element concentrations

AbstractnAn attempt to characterize natural graphites by their trace element content is reported. Ten samples of graphite of known deposits over the world are classified by their graphitization indices, ranging from 0.26 to 1.00, and analyzed for trace elements content. Results of neutron activation analysis of 28 evaluated elements, i.e. Na, Rb, Cs, Th, U, Cr, Fe, Co, As, Sb, Ag, Au, Se, Te, Zn, Hg, Zr, Hf, Ta, Sc, La, Ce, Nd, Sm, Eu, Tb,Yb and Lu, are presented and briefly discussed.