Abstract Transparent and clear glasses were prepared from fluorphlogopite-fluormuscovite system mixtures. Mica crystals were precipitated in the glass by later heat treatment. The mica crystals were identified as fluorphlogopite by x-ray powder diffraction patterns. An interlocking microstructure of mica was observed at above 800°C. The density of crystallized glass increased with increasing heat treatment temperatures. The density attained a maximum at about 900°C.