Which one of the following is not used as a raw material in the manufacture of glass?

Glass is primarily manufactured by melting a mixture of silica (sand), soda (sodium carbonate), and lime (calcium carbonate). Soda acts as a flux to lower the melting point of silica [2]. Alumina (aluminum oxide) is frequently added to improve the chemical durability and viscosity of the glass [1]. Borax (sodium borate) is a critical raw material for producing borosilicate glass, which is known for its thermal resistance [2]. In contrast, Gypsum (calcium sulfate dihydrate) is not a standard raw material for glass manufacture. While calcium compounds like lime are essential, they are typically introduced as carbonates or oxides [3]. Gypsum is primarily used in the production of cement, plaster of Paris, and wallboard rather than as a primary constituent in the glass-making process. Therefore, among the given options, gypsum is the one not used as a raw material for glass.

Sources

1. [2] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Uses of washing soda > p. 32
2. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 13: Types of Rocks & Rock Cycle > 13.5. Some Rock-Forming Minerals > p. 175
3. [3] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 8: Nature of Matter: Elements, Compounds, and Mixtures > Activity 8.1: Let us experiment > p. 118