The subbituminous kl seam in the Middle Miocene Soma Formation of western Turkey reaches a thickness of 24 m. Typical samples on an air-dried basis have 9.5-14.2% moisture, 4.3-13.8% ash and 0.57-2.54% total sulphur. The coal rank parameters and non-agglomerating behaviour show that the coals are of subbituminous A rank. The kl seam is huminite-rich coal with a mean random ulminite reflectance (%Rr) between 0.46 and 0.49%. Fluorescence emission measurements show that the sporinite, cutinite, resinite and alginite present have typical fluorescence spectra between 460 and 700 nm. The Soma Formation was intruded by an olivine basalt during the Pliocene-Pleistocene, which caused local contact metamorphism at the top of the kl seam. On the basis of proximate, ultimate and petrographic analyses the intruded seam can be divided into normal coal, transition zone and natural coke intervals, each differing in their degree of metamorphism. Moisture, volatile matter, hydrogen and oxygen contents very rapidly decrease close to the contact point with the intrusion, whilst calorific value, carbon content and mean random reflectance value increase. A diagram of O/C versus H/C also shows a distinct increase in rank caused by the intrusion. Minor illite, siderite and plagioclase feldspar are present in the natural coke samples, but pyrrhotite is not observed. Mineralogical, geochemical and reflectance studies indicate that the general temperature during formation of natural coke was probably relatively low (< 650 degrees C), with the coal also under the influence of stress. This relatively low coking temperature is thought to have been related to the insignificant volume and quick cooling of the basaltic magma, the high proportion of bed moisture in the coal and the poor thermal conductivity of the seam. (C) 1997 Elsevier Science B.V.