Abstract: Glass has optical constants of a refractive index (nd) of 1.79 or over and an Abbe number (?d) of 27 or over and a specific gravity (D) of 3.20 or over and is free from devitrification in the interior of the glass in a reheat test. The glass has chemical durability according to the Powder Method (acid-proof property RA according to the Powder Method) which is Class 1.

Abstract: An optical glass having optical constants of refractive index (nd) within a range from 1.49 to 1.54 and Abbe number (? d) within a range from 55 to 65 comprises, in mass %, SiO2 >65-75% R2O (R is at least one selected from the group ?15-25% consisting of Li, Na, K and Cs) where Li2O ?0.1-5.0% Na2O ?1.0-10.0% K2O ?5.0-20.0% and Cs2O ?0-5.0% R?O (R? is at least one selected from the group ?0.5-10% consisting of Mg, Ca, Sr or Ba) where MgO ?0-10% and/or CaO ?0-10% and/or SrO ?0-10% and/or BaO ?0-10% ZnO ?0-<3.0% and/or B2O3 ?0-6.0% and/or Al2O3 ?0-<1.0% and/or TiO2 ?0-<2.0% and/or ZrO2 ?0-2% and/or WO3 ?0-3.0% and/or Sb2O3 ?0-2.0% and a fluoride or fluorides of a metal element or ?0-2%.

Abstract: Glass has optical constants of a refractive index (nd) of 1.79 or over and an Abbe number (?d) of 27 or over and a specific gravity (D) of 3.20 or over and is free from devitrification in the interior of the glass in a reheat test. The glass has chemical durability according to the Powder Method (acid-proof property RA according to the Powder Method) which is Class 1.

Abstract: An optical glass having a small photoelastic constant (?) suitable for parts for polarizing optical system and light polarization control elements and having a refractive index (nd) within a range from 1.60 to 1.68 and an Abbe number (? d) within a range from 40 to less than 65 comprises, as atoms constituting the optical glass, P 5–10 mol % Al 1–3 mol % Ba 8–13 mol %, Gd 1–5 mol % Nb 0.1–3 mol % F 15–35 mol % and O 40–52 mol %.

Abstract: An optical glass having a small photoelastic constant (?) suitable for parts for polarizing optical system and light polarization control elements and having a refractive index (nd) within a range from 1.60 to 1.68 and an Abbe number (? d) within a range from 40 to less than 65 comprises, as atoms constituting the optical glass, P 5-10 mol % Al 1-3 mol % Ba 8-13 mol %, Gd 1-5 mol % Nb 0.1-3 mol % F 15-35 mol % and O 40-52 mol %.

Abstract: An optical glass having a positive anomalous dispersion comprises, in mass %, SiO2 40-60% B2O3 3-9% TiO2 ?3-15% Nb2O5 0.1-5.0% Al2O3 ?3-15% WO3 0.5-5.0% MgO 0-3% CaO 0-3% SrO 0-3% BaO 0-3% K2O exceeding 10% and up to 21% Na2O ?0-10% Sb2O3 0-1% and a fluoride or fluorides of a metal element or elements ??3-10%, contained in the above metal oxides, a total amount of F contained in the fluoride or fluorides is free of PbO and As2O3 except for unavoidable mixing of these compounds as impurities, has optical constants of a refractive index (nd) within the range from 1.48 to less than 1.55 and an Abbe number (?d) within the range from 45 to 55, and has an anomalous dispersion (??g,F) of +0.0010 or over.

Abstract: An optical glass having optical constants of refractive index (nd) within a range from 1.49 to 1.54 and Abbe number (? d) within a range from 55 to 65 comprises, in mass %, SiO2 >65-75% R2O (R is at least one selected from the group ?15-25% consisting of Li, Na, K and Cs) where Li2O ?0.1-5.0% Na2O ?1.0-10.0% K2O ?5.0-20.0% and Cs2O ?0-5.0% R?O (R? is at least one selected from the group ?0.5-10% consisting of Mg, Ca, Sr or Ba) where MgO ?0-10% and/or CaO ?0-10% and/or SrO ?0-10% and/or BaO ?0-10% ZnO ?0-<3.0% and/or B2O3 ?0-6.0% and/or Al2O3 ?0-<1.0% and/or TiO2 ?0-<2.0% and/or ZrO2 ?0-2% and/or WO3 ?0-3.0% and/or Sb2O3 ?0-2.0% and a fluoride or fluorides of a metal element or ?0-2%.

Abstract: An information storage disk holding member for holding an information storage disk in position in an information storage disk drive device, the holding member being made of glass-ceramics in which a crystal phase is dispersed in a glass matrix. The holding member has specific rigidity (Young's modulus/specific gravity) of not greater than 37 GPa, specific gravity of not greater than 3.0, coefficient of thermal expansion within a range from −50° C. to +70° C. which is within a range from +35×10−7/° C. to +130×10−7/° C., Young's modulus within a range from 95 GPa to 130 GPa, specific gravity within a range from 2.40 to 2.60 and bending strength within a range from 400 MPa to 800 MPa.

Abstract: There is provided a glass-ceramic which is suitable for use as a light filter. The glass-ceramic has Young's modulus (GPa) within a range from 95 to 120 and includes 5.3-8 weight percent of Al2O3, 0.5-3.5 weight percent of ZrO2 and 71-81 weight percent of SiO2, based respectively on the total content of the oxides. The glass-ceramic preferably has, as its predominant crystal phases, (a) lithium disilicate (Li2O.2SiO2) and (b) at least one of &agr;-quartz (&agr;-SiO2) and &agr;-quartz solid solution (&agr;-SiO2 solid solution), has specific gravity within a range from 2.4 to 2.6 and has a coefficient of thermal expansion within a range from 65×10−7/° C. to 130×10−7/° C. within a temperature range from −50° C. to +70° C.

Abstract: An optical glass includes SiO2; PbO; B2O3; not less than 0.1 mass % of TeO2; and not less than 0.4 mass % of Li2O.

Abstract: An optical glass having a positive anomalous dispersion comprises, in mass %, 1 SiO2 40-60% B2O3 3-9% TiO2  3-15% Nb2O5 0.1-5.0% Al2O3  3-15% WO3 0.5-5.

Abstract: There is provided a glass-ceramic substrate which is suitable for use as a light filter. The glass-ceramic has a Young's modulus (GPa) within a range from 95 to 120 and includes 5.3 to 8 weight percent (expressed on an oxide basis) of Al2O3. Tile glass ceramic substrate preferably has, as its predominant crystal phases, (a) lithium disilicate (Li2O·2SiO2) and b) at least one of &agr;-quartz (&agr;-SiO2) and &agr;-quartz solid solution (&agr;-SiO2 solid solution), has a specific gravity within a range from 2.4 to 2.6 and has a coefficient of thermal expansion within a range from 65×10−7/° C. to 130×10−7/° C. within a temperature range from −50° C. to +70° C.

Abstract: An information storage disk holding member for holding an information storage disk in position in an information storage disk drive device, the holding member being made of glass-ceramics in which a crystal phase is dispersed in a glass matrix. The holding member has specific rigidity (Young's modulus/specific gravity) of not greater than 37 GPa, specific gravity of not greater than 3.0, coefficient of thermal expansion within a range from −50° C. to +70° C. which is within a range from +35×10−7/° C. to +130×10−7/° C., Young's modulus within a range from 95 GPa to 130 GPa, specific gravity within a range from 2.40 to 2.60 and bending strength within a range from 400 MPa to 800 MPa.

Abstract: An optical glass includes SiO2; PbO; B2O3; not less than 0.1 mass % of TeO2; and not less than 0.4 mass % of Li2O.

Abstract: There is provided a glass-ceramic which is suitable for use as a light filter. The glass-ceramic has Young's modulus (GPa) within a range from 95 to 120 and includes 5.3-8 weight percent of Al2O3, 0.5-3.5 weight percent of ZrO2 and 71-81 weight percent of SiO2, based respectively on the total content of the oxides. The glass-ceramic preferably has, as its predominant crystal phases, (a) lithium disilicate (Li2O.2SiO2) and (b) at least one of &agr;-quartz (&agr;-SiO2) and &agr;-quartz solid solution (&agr;-SiO2 solid solution), has specific gravity within a range from 2.4 to 2.6 and has a coefficient of thermal expansion within a range from 65×10−7/° C. to 130×10−7/° C. within a temperature range from −50° C. to +70° C.

Abstract: A high rigidity glass-ceramic substrate is provided which contains, as a predominant crystal phase or phases, at least one crystal phase selected from the group consisting of enstatite (MgSiO3), enstatite solid solution (MgSiO3 solid solution), magnesium titanate (MgTi2O5) and magnesium titanate solid solution (MgTi2O5 solid solution), has fine crystal grains (preferably globular crystal grains) of precipitated crystal phases, has excellent melting property of a base glass, high resistivity to devitrification, easiness in polishing, excellent smoothness in the surface after polishing and has high Young's modulus capable of coping with a high speed rotation.

Abstract: A high rigidity glass-ceramic substrate is provided which contains, as a predominant crystal phase or phases, at least one crystal phase selected from the group consisting of enstatite (MgSiO3), enstatite solid solution (MgSiO3 solid solution), magnesium titanate (MgTi2O) and magnesium titanate solid solution (MgTi2O5 solid solution), has fine crystal grains (preferably globular crystal grains) of precipitated crystal phases, has excellent melting property of a base glass, high resistivity to devitrification, easiness in polishing, excellent smoothness in the surface after polishing and has high Young's modulus capable of coping with a high speed rotation.

Abstract: A glass-ceramic suitable for use as a light filter includes, as a predominant crystal phase, lithium disilicate (Li2O.2SiO2) or a combination of lithium disilicate and at least one crystal phase selected from the group consisting of &agr;-quartz (&agr;-SiO2), &agr;-quartz solid solution (&agr;-SiO2 solid solution), &agr;-cristobalite (&agr;-SiO2) and &agr;-cristobalite solid solution (&agr;-SiO2 solid solution). This substrate has Young's modulus (GPa)/specific gravity of 37 or over, surface roughness Ra (arithmetic mean roughness) of 5.0 Å or below, a coefficient of thermal expansion within a temperature range from −50° C. to +70° C. which ranges from +65×10−7/° C. to +130×10−7/° C. and bending strength of 400 MPa or over.

Abstract: There is provided a glass-ceramic substrate for an information storage medium usable in an information storage device of the ramp loading system. The glass ceramic substrate has a Young's modulus (GPa)/specific gravity of 37 or over and includes 5.3 to 8 weight percent (expressed on an oxide basis) of Al2O3. The glass ceramic substrate has, as its predominant crystal phases, lithium disilicate (Li2O.2SiO2) and &agr;-quartz (&agr;-SiO2), has a coefficient of thermal expansion within a range from 65×10−7/° C. to 130×10−7/° C. within a temperature range from −50° C. to +70° C. and has a surface roughness (Ra) (arithmetic mean roughness) of 9 Å or below.

Abstract: A high rigidity glass-ceramic substrate is provided which contains, as a predominant crystal phase or phases, at least one crystal phase selected from the group consisting of enstatite (MgSiO), enstatite solid solution (MgSiO3 solid solution), magnesium titanate (MgTi2O5) and magnesium titanate solid solution (MgTi2O5 solid solution), has fine crystal grains (preferably globular crystal grains) of precipitated crystal phases, has excellent melting property of a base glass, high resistivity to devitrification, easiness in polishing, excellent smoothness in the surface after polishing and has high Young's modulus capable of coping with a high speed rotation.