Phase separation could be observed in a base glass from the system SiO2-Al2O3-Na2I-K2O-CaO-P2O5-F-. Both surface and volume crystallization of leucite and apatite, respectively, were found after heat treatment of the powdered and sintered material at temperatures between 850 degrees C and 1150 degrees C. After removing the leucite crystals from monolithic blocks, which were cast and heat treated at temperatures between 580 degrees C and 800 degrees C for 8 hour only apatite crystallisation in the volume could be found. Optical microscopy (Zeiss: Jenaplan), X-ray diffraction (siemans: D5000), scanning electron microscopy (zeiss: DSM 940A), AFM (ultraobjektiv:SIS), and transmission electron microscopy/electron diffraction (Hitachi: H8100) were used to characterise the phase content of the glass ceramic material.
