The reaction is catalyzed by phosphoric acid or sulfuric acid. Tricalcium phosphate is produced commercially by treating hydroxyapatite with phosphoric acid and slaked lime. Iron, zinc or manganese phosphate salts are dissolved in a solution of phosphoric acid. These include mixtures of phosphoric and hydrofluoric acids as well as surfactants. For example, triphenyl phosphate is the ester derived from phosphoric acid and phenol. Various calcium phosphate minerals are used in the production of phosphoric acid and fertilizers. Monopotassium phosphate is produced by the action of phosphoric acid on potassium carbonate. Fluorine gas is made from hydrofluoric acid produced as a by-product in phosphoric acid manufacture. The C-3 hydroxyl group is esterified to phosphoric acid. This white crystalline solid is the anhydride of phosphoric acid. Polyphosphates arise by polymerization of phosphoric acid derivatives. They are oxidized to phosphoric acid or its salts. The salt is obtained by partial neutralization of phosphoric acid. Industrially, the mineral is an important source of both phosphoric and hydrofluoric acids. Processing phosphate ore into fertilizers and phosphoric acid for export is a major economic activity.