Disclosed is a substantially transparent glass-ceramic ceramic, and a method for making a glass-ceramic, exhibiting an aluminogallate spinel crystal phase and having a glass-ceramic composition that lies within the SiO₂-Al₂O₃-ZnO-K₂O-Ga₂O₃-Na₂O system and particularly consisting essentially, in weight percent on an oxide basis, of 25-50% SiO₂, 15-45% ZnO, 0-26% Al₂O₃, 0-25% K₂O, 0-10% Na₂O, 0-32% Ga₂O₃, a K₂O+Na₂O amount of greater than 10%, a Al₂O₃+Ga₂O₃ of greater than 10%, the glass ceramic microstructure containing a crystal phase comprising at least 15%, by weight, of hexagonal ZnO crystals. Another aspect disclosed is optical element selected from the group consisting of an optical fiber, a gain or laser medium, and an amplifier component, a saturable absorber, with the element comprising a transparent glass-ceramic of the same composition and containing a crystallinity of at least about 15% by weight of hexagonal ZnO crystals.