Crystalluria Uric acid crystalluria 2020-04-25T12:31:17Z Uric acid crystals are very pleiomorphic, but the rhomboidal shape is the most frequent. Distinctive morphological features are the amber color and the constant polychromatic birefringence. These crystals can be found both in normal subjects as well as in stone formers. Moreover, they can be found, alone or with amorphous urates in patients with increased purine metabolism. The presence of uric acid crystals in the urine.