Pyroxenic basalt-based glass /mullite composites were prepared. The effect of sintering temperatures on crystallized phases were studied by X-ray diffraction pattems; also the details of microstructure and mineralogical constituents were examined by using SEM. The crystallization of augite ss and mullite at low temperature and plagioclase and spinel at higher temperature were observed. Apparent porosity and relative density of the sintered samples were also measured. Measurements of dielectric constants showed preparation of good insulators of samples containing plagioclase and spinel phases.