During the exploitation of the Bełchatów lignite deposit at the point of contact between Mesozoic substrate and Neogene deposits, rocks of different petrographic composition were found. The group of rocks with transitional features between carbonate and silica rocks were called opoka-rock. This article presents the current state of knowledge on the geological conditions of occurrence of the Bełchatów opoka-rock, and on its petrographic and chemical characteristics. An analysis was also carried out to determine physical, mechanical as well as raw-material properties, as well as the related issue of potential utilisation