Glass-ceramic materials were produced from fly ash samples obtained from the Seyitomer thermal power plant in Turkey. Glass samples were crystallized by suitable nucleation and crystal growth heat treatments on the basis of DTA results. The microstructural analysis of glass-ceramic samples were carried out using SEM and XRD techniques. SEM investigations clearly demonstrated the presence of a tiny crystallized phase dispersed in the microstructure. XRD results revealed that the main crystalline phase was diopside [Ca(Mg,Al)(Si,Al)(2)O-6], It was observed that the mechanical properties and the thermal expansion coefficient of the glass-ceramic samples depend only on the amount of the crystalline phase. Furthermore, chemical durability of the produced glass-ceramic samples were high. (C) 2002 Elsevier Science Ltd. All rights reserved.