A mineable lignite bed (k1) in the Soma Formation from the southern part of the Soma basin is of middle Miocene age and was deposited in a lacustrine environment. Its thickness reaches up to 24 m, and it is extensively mined by open-pit methods. The Soma Formation was invaded by an olivine basaltic intrusion during the Pliocene-Pleistocene. The intrusion has resulted in a local contact metamorphic influence at the top level of the k1. The coal bed, on the basis of proximate analyses and random reflectance measurement (Ro, random) of huminite/uitrinite of coals or groundmass of cokes, can be divided into normal coal, transition zone, and natural coke, differing in their degree of coal metamorphism. Closer to the contact point with the intrusion, moisture and volatile matter contents rapidly decrease,while calorific value and the %Ro, random values increase.