Studies on the morphology of human uric acid stones.

Human uric acid acid renal stones are easily distinguished from other urinary calculi by their globular or spherical shape, their colour and their hardness. Investigations of uric acid crystals grown in the presence of a variety of pigments indicate that a disordered layer structure of the uric acid dihydrate is responsible for the colour of such crystals, caused by the inclusion of pigment molecules into the crystal lattice. This in turn may help to explain the other special properties of uric acid stones.