Patent ID: 8603653

Claim:
A glass for a magnetic recording medium substrate, which comprises, denoted as molar percentages, 50 to 75 percent of SiO 2 , 0 to 2.1 percent of Al 2 O 3 , 0 to 3 percent of Li 2 O, 0 to 5 percent of ZnO, a total of Na 2 O and K 2 O of 3 to 15 percent, a total of MgO, CaO, SrO, and BaO of 14 to 35 percent, a total of ZrO 2 , TiO 2 , La 2 O 3 , Y 2 O 3 , Yb 2 O 3 , Ta 2 O 5 , Nb 2 O 5 , and HfO 2 of 2 to 9 percent, with a molar ratio of {(MgO+CaO)/(MgO+CaO+SrO+BaO)} falling within a range of 0.85 to 1, and a molar ratio of {Al 2 O 3 /(MgO+CaO)} falling within a range of 0 to 0.30, wherein the glass is an amorphous glass.