Patent ID: 7008891

Claim:
A crystallized glass for an optical filter substrate, which consists, as represented by mol % based on the following oxides, essentially of: SiO 2 : 30 to 65%, Al 2 O 3 : 5 to 35%, TiO 2 +ZrO 2 : 1 to 15%, Na 2 O: 0 to 30%, K 2 O: 5 to 30%, provided K 2 O (%)≧Na 2 O (%), Li 2 O: 0 to 15%, MgO: 0 to 15%, CaO: 0 to 15%, SrO: 0 to 15%, BaO: 0 to 15%, ZnO: 0 to 15%, B 2 O 3 : 0 to 15%, P 2 O 5 : 0 to 15%, Y 2 O 3 : 0 to 15%, and which has an average linear expansion coefficient α L of from 95×10 −7 /° C. to 130×10 −7 /° C. at from −30° C. to 70° C., and which has a crystal or solid solution of Na 4-x K x Al 4 Si 4 O 16 (1<x≦4) precipitated therein.