Phosphate optical glass, preform for precision press molding and manufacturing method of the same, optical element and manufacturing method of the same

Phosphate optical glass having an Abbé number, νd, of greater than 59 and less than 70, comprising the following components, denoted as mass percentages:

• P2O5:
• 18 to 70 percent, where 70 percent is excluded;
• B2O3:
• 0.6 to 34 percent, where P2O5/B2O3, as a mass percentage ratio, is 2.04 to 30;
• Al2O3:
• 0 to 8 percent;
• Li2O:
• 0 to 20 percent, where 0 percent is excluded;
• Na2O:
• 0 to 18 percent;
• K2O:
• 0 to 15 percent;
• MgO:
• 0 to 25 percent;
• CaO:
• 0 to 18 percent, where MgO+CaO>4 percent;
• SrO:
• 0 to 20 percent;
• BaO:
• 0 to 40 percent, where SrO+BaO>1 percent and BaO/B2O3, as a mass percentage ratio, is 0 to 15;
• ZnO:
• 0 to 14 percent,
• where the ratio of ΣR″O/ΣR′O as a mass percentage ratio is less than 23, where ΣR″O═MgO+CaO+SrO+BaO+ZnO and ΣR′O═Li2O+Na2O+K2O;
• Gd2O3:
• 0 to 18 percent;
• Sb2O3:
• 0 to 1 percent;
• wherein any other component besides those listed above has a content lower than the content of B2O3 as well as lower than the content of Li2O.