MINERALOGICAL COMPONENTS OF SOME THERMALLY DECOMPOSED LIGNITE AND LIGNITE ASH FROM THE PTOLEMAIS BASIN, GREECE

Two samples of Pliocene lignites from the Ptolemais basin of Greece, o ne from the upper and one from the lower lignite seams, were heated an d dried in air at 50 degrees C intervals from 50 to 1200 degrees C. Th e two lignite samples initially contained the same minerals, namely ca lcite, dolomite, quartz, kaolinite, illite, pyrite and gypsum, but in different proportions. The lignite sample from the upper lignite seam is rich in Fe2O3, CaO and SO3, while that from the lower lignite seam is rich in SiO2 and Al2O3. Hematite, periclase, melilites, merwinite, calcium ferrite and brownmillerite are constituents of the 1200 degree s C lignite ash from both samples. The heating conditions and the chem istry of the samples lowered the formation temperatures of brownmiller ite, which appeared in both samples at 950 degrees C. In the Fe2O3, Ca O- and SO3-rich sample, magnesioferrite is present from 850 to 1100''C and hematite appears at 300 degrees C. In the SiO2- and Al2O3-rich sa mple, magnesioferrite was not detected at any temperature and hematite appeared at 600 degrees C. Anhydrite, which normally decomposes in ai r at 1638 degrees C, is the main constituent at 1150 degrees C, on hea ting the lignite sample that was rich in Fe2O3, CaO and SO3. Anhydrite diminishes at 1200 degrees C. In the SiO2- and Al2O3-rich lignite sam ple, anhydrite is main constituent at 1100 degrees C, but diminishes c onsiderably at 1150 degrees C and decomposes at 1200 degrees C.