Researches of crystals consisting of IVth group element (C, Si, Ge and Sn) polyhedra are described. Fundamental concept for understanding the structure and the electronic properties of the polyhedral clusters and crystals is given. The different structure of the crystals of C and Si is emphasized focusing on van der Waals and covalent characters. Applications of cluster crystals colored by elemental isotopes are also demonstrated in connection to materials science and future electronic devices.
