Optical glass

1. An optical glass that is an oxide glass and that comprises, by cationic %,

0 to 30% of Si 4+ ,

10 to 55% of B 3+ ,

less than 5% of total of Li + , Na + and K + ,

less than 5% of total of Mg 2+ , Ca 2+ and Sr 2+ ,

0 to 8% of Ba 2+ ,

0.1 to 15% of Zn 2+ ,

22 to 50% of La 3+ ,

0 to 20% of Gd 3+ ,

0 to 15% of Y 3+ ,

0 to 10% of Yb 3+ ,

0 to 20% of Zr 4+ ,

0.1 to 22% of Ti 4+ ,

0 to 20% of Nb 5+ ,

0 to 8% of Ta 5+ ,

0 to 5% of W 6+ ,

0 to 8% Ge 4+ ,

0 to 10% of Bi 3+ , and

0 to 10% of Al 3+ ,

the cationic ratio of the content of Si 4+ to the content of B 3+ , Si 4+ /B 3+ , being less than 1.0, the optical glass having a refractive index nd of 1.930 to 2.2, an Abbe's number νd of 26 to 45 and a glass transition temperature which is higher than 630° C.

2. The optical glass of claim 1 , which has a coloring degree λ70 of less than 470 nm.

3. The optical glass of claim 1 , which has a partial dispersion ratio Pg,F and an Abbe's number νd which satisfy the relationship of the following expression (1),

Pg,F≦− 0.0017 ×νd+ 0.660  (1).

4. A press-molding glass gob formed of the optical glass recited in claim 1 .

5. An optical element which is formed of the optical glass recited claim 1 .

6. A process for producing an optical element blank to be completed into an optical element by grinding and polishing, which comprises softening the press-molding glass gob recited in claim 4 by heating, and press-molding it.

7. A process for producing an optical element blank to be completed into an optical element by grinding and polishing, which comprises melting a glass raw material and press-molding the thus-obtained molten glass to produce an optical element blank formed of the optical glass recited in claim 1 .

8. A process for producing an optical element, which comprises grinding and polishing the optical element blank recited in claim 6 .

9. A process for producing an optical element, which comprises grinding and polishing the optical element blank recited in claim 7 .