Crystallography of tetracalcium phosphate

Abstract

Tetracalcium phosphate, Ca4O(PO4)2, has a monoclinic modification with the parameters a= 11.99, b = 9.48, and c = 6.97 A, α = 90.8°, z = 4, and space group P21 or P21/m. From a comparison with the work of Trömel and Zaminer, it is concluded that this salt has monoclinic and orthorhombic modifications with the most probable space groups being P21 and P21221, respectively. The results support the view that tetracalcium phosphate has a layer-type structural relationship to hydroxyapatite, Ca5(OH)(PO4)3. This would account, in part, for variations in the compositions of apatitic materials in which the ratio Ca/P is greater than 10/6, and it suggests that tetracalcium phosphate may be present in the mineral of tooth and bone.