This study focuses on the geochemical and mineralogical compounds of clay occurrences that had been interbedded low rank coals in Biga Peninsula, Turkey. The usages of these clay formations were also studied. Clay occurrences were formed and alternated along with Tertiary lignite seams in the peninsula where is one of the basic metallic and industrial mineral potential regions in Turkey. Chemical and mineralogical analyses were performed on thirteen clay samples from different lignite beds. The XRD analyses show that while kaolin group minerals are dominant in almost all areas, especially middle and western parts of the peninsula, smectite group clays are mostly observed in the eastern part. Alkaline feldspar, plagioclase, quartz, micas and mixed-layered clays were other determined minerals. The contents of major elements were detected by XRF method and the analyses exhibit that SiO2 and Al2O3 are the main components in all deposits. SiO2 ratio is between 55.0% and 64.5%, while Al2O3 percentage is 16.5% 25.5% in general. The contents of K2O, Na2O, CaO and MgO change in low range. Titanium oxide (TiO2) ratio is up to 1.3%. Iron oxide (Fe2O3) is changing from 0.5% to 6.5%. In spite of the fact that SiO2 and Al2O3 concentrations are suitable for industrial usage, because of undesirable substances. The presence industrial important is controversial.