the instant invention is drawn to glass - ceramics especially designed for the fabrication of radomes , wherein cordierite is the predominant crystal phase but which also contain minor amounts of cristobalite , magnesium - aluminum titanate , and rutile , having overall compositions consisting essentially , expressed in weight percent on the oxide basis , of about ______________________________________ mgo 15 - 18 al 2 o 3 21 - 25 sio 2 48 - 53 tio 2 9 . 5 - 11 . 5 as 2 o 3 0 - 1______________________________________