9. Glass industry

Glasses result from the fusion of an intimate mixture of mineral materials, the main element of which is silica. The added elements are CaO, MgO, Al ₂ O ₃ , K ₂ O, Na ₂ O and B, which are contributed by limestone, dolomite, phonolite, nepheline syenite, feldspar, borax, colemanite and gypsum. Sodium salts (carbonates and sulfates), alumina (in the broadest sense) and salts of Ni, Co, Fe, Se, Pb, Li and Ce are also used, depending on the glass grade. Silica and feldspar must be reduced to 800 µm, other minerals...