Calcium Pyro- and Meta- niobates

A calcium columbate is present in the mineral pyrochlore. If niobatic acid, potassium chloride, and a large excess of calcium fluoride are fused together at bright red heat for several hours, calcium pyroniobate, Ca₂Nb₂O₇, is obtained in orthorhombic prisms. If the potassium chloride is in excess, the metaniobate, Ca(NbO₃)₂, is formed in long, thin needles. The pyroniobate may also be obtained by precipitating a solution of calcium chloride with potassium niobate, fusing the precipitate with anhydrous calcium chloride, and lixiviating with water, whilst the metaniobate is prepared by fusing the precipitated salt with boric acid and lixiviating with dilute hydrochloric acid. The density of the latter is 4.12.