The result of the cooperation of several compounds is the complex of characteristic features of clays – first of all the size of crystalls, their morphology and crystallo-chemical composition. Specific features of clays, mainly the ability of isolation predetermine them for utilization in protection of the environment. The function of barriers is to create a mechanical and chemical zone preventing the penetration of underground waters, waste waters, and waste materials into the surroundings. Clays are suitable as deposits of various wastes, stemming and lining of bore holes, hollows, tunnels etc. From this point of view raw materials base of Slovakia is ideal especially for barriers.