The correct answer is gypsum. Key Points - Glass is formed when molten material is cooled so quickly that its constituent atoms do not have time to align themselves into an ordered lattice. - Soda ash varies in density, size, and shape when mined and processed. - This flexibility allows it to be used in a variety of everyday products like glass. - Specifically, soda ash is used to make the most common type of glass, soda-lime silica glass. - It is used as the main ingredient because soda ash naturally reduces melting temperatures and its alkali effectively supports the shaping of the glass item. - Alumina is used in glassmaking because of its superior mechanical and optical properties. - Alumina can form glass if it is alloyed with calcium or rare-earth oxides. - But the required quenching rate can be as high as 1000 degrees per second, which makes it difficult to produce bulk quantities. - Glass manufacturers add borax to the silica base to: - significantly lower melting temperature and viscosity, inhibit crystallization of the glass, control thermal expansion, and inhibit devitrification. - The resulting products have inherent durability and chemical resistance and are tough enough to withstand considerable mechanical or thermal shock.