The present invention relates to crystallizates of the pure aminoalkylenephosphonic acid DTPMP in three crystal polymorphs and to a process for obtaining solid crystalline DTPMP by a preferably one-stage crystallization from an aqueous product mixture comprising DTPMP, wherein the process comprises the following process steps: (a) introducing seed crystals comprising DTPMP into an aqueous crude product comprising DTPMP with a total proportion in the range from 10 to 65 percent by mass up to a suspension density in the range from 1% to 25%; (b) introducing kinetic energy into the aqueous crude product to precipitate a crystallizate containing DTPMP as pure acid with a total content of at least 75% by mass; and (c) removing the crystallizate formed from the aqueous crude product by sedimentation and/or filtration, such that DTPMP is obtained as a solid end product in the form of a crystallizate.