Abstract: Provided is an inorganic composition article that is hard and highly transparent. The inorganic composition article includes at least one type selected from ?-cristobalite and an ?-cristobalite solid solution as a main crystal phase, has a coloring degree ?80 of 330 to 580 nm at a thickness of 10 mm, and has a Vickers hardness of 620 or more.

Abstract: Provided is reinforced crystallized glass that has a high strength and is less likely to break. The reinforced crystallized glass includes a compressive stress layer on a surface, and [CS50 ?m*(DOLzero?50)]/2 is 2000 or more, where CS50 ?m (MPa) is a compressive stress at a depth of 50 ?m from an outermost surface, and DOLzero (?m) is a stress depth when the compressive stress is 0 MPa.

Abstract: Provided are crystallized glass that is easy to process and in which a high compressive stress value can be obtained on a surface, and reinforced crystallized glass thereof. A crystallized glass containing at least one type selected from ?-cristobalite and an ?-cristobalite solid solution as a main crystal phase, in which, by mass % in terms of oxide, a content of a SiO2 component is 50.0% to 75.0%, a content of a Li2O component is 3.0% to 10.0%, a content of an Al2O3 component is 5.0% or more and less than 15.0%, and a content of a B2O3 component is more than 0% and 10.0% or less.

Abstract: Provided is a chemically strengthened optical glass with improved crack resistance and high hardness, in which the refractive index and the Abbe number required for a conventional optical glass are maintained. The chemically strengthened optical glass includes a compressive stress layer on a surface, and contains, by mass % in terms of oxide: 2.0 to 20.0% of a SiO2 component, 5.0 to 35.0% of a B2O3 component, 20.0 to 60.0% of a La2O3 component, 2.0 to 25.0% of a TiO2 component, 2.0 to 15.0% of a Nb2O5 component, and more than 0% to 10.0% of a LiO2 component, and the chemically strengthened optical glass is characterized in that an Hv change rate defined as [(Hvafter?Hvbefore)/Hvbefore]×100 is equal to or greater than 3.0%.

Abstract: Provided is a chemically strengthened optical glass with improved crack resistance and high hardness, in which the refractive index, the Abbe number, and the transmittance required for a conventional optical glass are maintained. The chemically strengthened optical glass includes a compressive stress layer on a surface, and contains, by mass % in terms of oxide: 20.0% to 50.0% of a SiO2 component, 10.0% to 45.0% of a TiO2 component, and 0.1 to 20.0% of a Na2O component, and the chemically strengthened optical glass is characterized in that an Hv change rate defined as [(Hvafter?Hvbefore)/Hvbefore]×100 is equal to or greater than 3.0%.

Abstract: A glass ceramic for an optical filter and an optical filter are obtained that have both thermal expansion characteristics for preventing refractive index fluctuations at a usage temperature of a filter member and mechanical characteristics considering durability, and further have excellent workability. An internal transmittance of the glass ceramic for an optical filter is 0.970 or more with respect to light having a wavelength of 1550 nm when a thickness of the glass ceramic is 1 mm. The glass ceramic includes, by mass % in terms of oxide, 40.0% to 70.0% of a SiO2 component, 11.0% to 25.0% of an Al2O3 component, 5.0% to 19.0% of a Na2O component, 0% to 9.0% of a K2O component, 1.0% to 18.0% of one or more components selected from a MgO component and a ZnO component, 0% to 3.0% of a CaO component, and 0.5% to 12.0% of a TiO2 component.