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Abstract

A glass substrate for use as the substrate of an information recording medium such as a magnetic disk, magneto-optical disk, DVD, or MD or of an optical communication device, and a glass composition for making such a glass substrate, contains the following glass ingredients: 45 to 75% by weight of SiO.sub.2; 1 to 20% by weight of Al.sub.2O.sub.3; 0 to 8% by weight, zero inclusive, of B.sub.2O.sub.3; SiO.sub.2+Al.sub.2O.sub.3+B.sub.2O.sub.3 accounting for 60 to 90% by weight; a total of 0 to 20% by weight, zero inclusive, of R.sub.2O compounds, where R=Li, Na, and K; and a total of 0 to 15% by weight, zero inclusive, of TiO.sub.2+ZrO.sub.2+Ln.sub.xO.sub.y, where Ln.sub.xO.sub.y represents at least one compound selected from the group consisting of lanthanoid metal oxides, Y.sub.2O.sub.3, Nb.sub.2O.sub.5, and Ta.sub.2O.sub.5.

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