The present invention is directed to the preparation of two groups of transparent glass-ceramics exhibiting high optical clarity and containing essentially only one crystal phase. The first group consists essentially, in cation percent, of

    ______________________________________
    SiO.sub.2
             20-35          PbF.sub.2
                                   19-23
    AlO.sub.1.5
             10-20          YF.sub.3
                                    3-7,
    CdF.sub.2
             19-34
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and the second group consists essentially, in cation percent, of ______________________________________ SiO.sub.2 20-35 PbF.sub.2 15-25 AlO.sub.1.5 10-20 YF.sub.3 3-7 CdF.sub.2 21-31 ZnF.sub.2 3-7. ______________________________________ These glass-ceramics may be used to fabricate optical waveguide fibers. Also when doped with certain rare earth elements, notably Pr, Er, and Dy, the glass-ceramic materials may be used to fabricate optical amplifiers and lasers.