A production process for producing high-purity silica from a crude silica source by means of fluosilic acid, including the steps of: (a) subjecting the crude silica souce and the fluosilicic acid to a reaction in a reaction stage, so as to produce silicon tetrafluoride and water; (b) selectively evaporating the silicon tetrafluoride with respect to at least a portion of at least one impurity derived from the crude silica source, and (c) reacting the silicon tetrafluoride with water to produce the high-purity silica, wherein the reaction stage (a) is performed at a temperature above 75.degree. C.