An aluminosilicate glass composition comprising: (a) 10-35% by weight of silica; (b) 10-35% by weight of alumina; (c) 3-30% by weight of zinc oxide; (d) 4-30% by weight P205; and (e) 3-25% by weight of fluoride which contains at most 3% by weight of alkaline metals calculated as M20, wherein M is Li, Na, and/or K, and wherein the weight ratio of the sum of zinc oxide and fluoride to P205 of from 0.8 to 3.0.