Formation of renal calculi can be caused by various dietary disturbances, being influenced by disorders of metabolic conditions such as hypercalcemia (hypertiroidism), hyperoxaluria (dietary, enteric, primary), hypocytruria, hyperuricosuria, etc. In this article, a number of structural parameters of renal calculi with binary composition oxalates - urates have been analysed by adequate techniques: X-ray diffraction, FT-IR spectroscopy, optical microscopy and SEM/EDS. For the biggest urolits a detailed analysis on radial differentiated sections has been performed with the aim to identify the initiator role in nucleation process and to find out the mechanism and the main steps in calculi growth.