Method of preparing a glass batch for melting silicate glass

A method of preparing a glass batch for melting silicate glass having an SiO.sub.2 content over 51% and a low alkali metal oxide content of up to 2% which comprises grinding batch ingredients based on rocks and mixing said ingredients with a flux comprising high-modulus calcium-magnesium hydrosilicate x.CaO.y.MgO.n.SiO.sub.2 m.H.sub.2 O wherein the SiO.sub.2 :CaO.MgO ratio is from 0.5 to 8 wherein the flux is produced by mixing silica, magnesia and calcia forming materials in an aqueous medium, heating the mixture to a temperature of 50.degree.-200.degree.C, holding the mixture at said temperature for at least 20 minutes, filtering and drying the resulting residue consisting of a high modulus calciummagnesium hydrosilicate.