An aluminosilicate glass having a composition consisting essentially of, as calculated in weight percent on an oxide basis, of 58-70% SiO.sub.2, 12-22% Al.sub.2O.sub.3, 3-15% B.sub.2O.sub.3, 2-12% CaO, 0-3% SrO, 0-3% BaO, 0-8% MgO, 10-25% MCSB (i.e., MgO+CaO+SrO+BaO), and SrO and BaO in combination being less than 3%.