Natural as well as synthetic, zeolites are used on a large scale. A third type of zeolites can be produced from waste products. Experiments on the formation conditions of zeolites have shown that waste products rich in highly reactive Si- and Al-containing materials are apt starting materials for zeolite formation. The use of waste materials, which consequently have to be looked upon as secondary raw materials, is not only noteworthy but also more and more necessary and paying because the opening up of new natural sources will become difficult in future, whereas at the same time protection of the environment is of growing importance. The aims of these types of experiments are to investigate what zeolite can be formed from these waste materials by treating them at different conditions. Special efforts are to be made to prepare commercially useful zeolites, to optimize the zeolite contents and the amount of the synthetic products, and to optimize the reaction process itself.