Magnetic-disk glass substrate, magnetic-disk glass substrate intermediate, and method for manufacturing magnetic-disk glass substrate

The glass substrate intermediate according to claim 7, wherein

• the glass composition that constitutes the glass substrate intermediate includes SiO2, Al2O3, MgO and CaO, with, in terms of oxide amount in mass %, Al2O3 in an amount of 15% to 23.5%, MgO in an amount of 2 to 20%, and CaO in an amount of 0.1 to 40%, with
• [SiO2(mass %)]+0.43×[Al2O3(mass %)]+0.59×[CaO(mass %)]−74.6≤0,
• and
• [SiO2(mass %)]+0.21×[MgO(mass %)]+1.16×[CaO(mass %)]−83.0≤0
• being satisfied.

A magnetic-disk glass substrate containing an alkaline earth metal component as a glass composition, the magnetic-disk glass substrate comprising:

• a pair of main surfaces;
• and
• an outer circumferential side edge surface that is a mirror surface, wherein
• the outer circumferential side edge surface includes a surface having a roughness percentage of 40% or more and 68% or less when a bearing ratio of a roughness cross-sectional area is 50% in a bearing ratio curve of roughness cross-sectional areas obtained when a surface roughness of the outer circumferential side edge surface obtained after the outer circumferential side edge surface is etched by 2.5 μm is measured,
• the glass composition that constitutes the magnetic-disk glass substrate includes SiO2, Al2O3, MgO and CaO, with, in terms of oxide amount in mass %, Al2O3 in an amount of 15% to 23.5%, MgO in an amount of 2 to 20%, and CaO in an amount of 0.1 to 40%, with
• [SiO2(mass %)]+0.43×[Al2O3(mass %)]+0.59×[CaO(mass %)]−74.6≤0,
• and
• [SiO2(mass %)]+0.21×[MgO(mass %)]+1.16×[CaO(mass %)]−83.0≤0
• being satisfied.

A glass substrate intermediate containing an alkaline earth metal component as a glass composition and serving as a blank for a magnetic-disk glass substrate, the glass substrate intermediate comprising:

• a pair of main surfaces;
• and
• an outer circumferential side edge surface that is a mirror surface, wherein
• the outer circumferential side edge surface includes a surface having a roughness percentage of 40% or more and 68% or less when a hearing ratio of a roughness cross-sectional area is 50% in a bearing ratio curve of roughness cross-sectional areas obtained when a surface roughness of the outer circumferential side edge surface obtained after the outer circumferential side edge surface is etched by 2.5 μm is measured,
• a glass transition point of the glass composition that constitutes the glass substrate intermediate is 700° C. or more, and
• the glass composition that constitutes the glass substrate intermediate is alkali-free glass.