| 摘要 |
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</SUB>; 1 to 20% by weight of Al<SUB>2</SUB>O<SUB>3</SUB>; 0 to 15% by weight, zero inclusive, of B<SUB>2</SUB>O<SUB>3</SUB>; SiO<SUB>2</SUB>+Al<SUB>2</SUB>O<SUB>3</SUB>+B<SUB>2</SUB>O<SUB>3 </SUB>accounting for 65 to 90% by weight; a total of 7 to 20% by weight of R<SUB>2</SUB>O compounds, where R=Li, Na, and K; and a total of 0 to 12% by weight, zero inclusive, of R'O compounds, where R'=Mg, Ca, Sr, Ba, and Zn. Moreover, the following conditions are fulfilled: B<SUB>2</SUB>O<SUB>3</SUB>=0% by weight, or Al<SUB>2</SUB>O<SUB>3</SUB>/B<SUB>2</SUB>O<SUB>3</SUB>>=1.0; and (SiO<SUB>2</SUB>+Al<SUB>2</SUB>O<SUB>3</SUB>+B<SUB>2</SUB>O<SUB>3</SUB>)/(the total of R<SUB>2</SUB>O compounds+the total of R<SUB>2</SUB>O compounds)>=3.
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