The mineralogy of the Neogene lacustrine facies of Pelitçik basin was investigated for the purpose of deriving the palaeoenvironmental parameters of this intervolcanic basin. The laboratory studies indicate that dolomite and K-feldspar are the major non-clay minerals in the study area, where plagioclase, analcime, fibrous zeolite and quartz are the minor constituents. Dolomites are found to be non-stoichiometric in chemistry. The clay fraction of the lacustrine facies is composed mainly of dioctahedral smectites. The smectites are rich in Al-Fe indicating a detrital origin. Illite comprises a minor contribution to the clay fraction, where chlorite and kaolinite are found in trace amounts. Based on dolomite stoichiometry and the mineral paragenesis found in the Pelitçik basin, the depositional conditions are suggested to have been a shallow, quiet, perennial lacustrine environment with fresh to slightly saline and slightly alkaline water chemistry. In addition, based on geological and mineralogical constraints, it is suggested that the water chemistry fluctuated during the deposition of the Pazar formation and the lake began its evolution with a hydrologically closed system and completed its evolution with a hydrologically open system.