Amorphous Al(n-x)(NH4)(3(1-x))(PO4)(n-y)(OH)(3(1-y)) (n = 1 or 2, x > 0, y <= 1) hydrate was prepd. by reaction of (NH4)(3)PO4, Al-2(SO4)(3) and aq. NH3 according to exptl. design, filtered off, dried and studied for chem. compn., sp. surface and oil absorption no. The product met the quality requirements for inorg. pigments.