Gypsum [has many uses] including making writing chalk, soil conditioning for agriculture, making moulds for pottery, as an additive in the manufacture of Ordinary Portland Cement (OPC), in surgical splints, in increasing the hardness of water, as an additive in certain foods such as tofu and in some types of medicines and pharmaceuticals. Its construction uses can also include external applications, such as in making walling blocks, where the climate is generally dry and not prone to the dampness that damages common types of gypsum.