X-ray powder diffraction was used to study the phase composition of human renal calculi. The stones were collected from 56 donors in Vitória, Espírito Santo state, southeastern Brazil. An XRD phase quantification revealed that 61% of the studied renal stones were composed exclusively of calcium oxalate ͓34% formed only by calcium oxalate monohydrate ͑COM͒ and 27% presents both monohydrate and dihydratate calcium oxalate͔. The 39% multi-composed calculi have various other phases such as uric acid and calcium phosphate. Rietveld refinement of XRD data of one apparent monophasic ͑COM͒ renal calculus revealed the presence of a small amount of hydroxyapatite. The presence of this second phase and the morphology of the stone ͑ellipsoidal͒ indicated that this calculus can be classified as non-papillary type and its nucleation process developed in closed kidney cavities. In order to show some advantages of the X-ray powder diffraction technique, a study of the phase transformation of monohydrate calcium oxalate into calcium carbonate ͑CaCO 3 ͒ was carried out by annealing of a monophasic COM calculi at 200, 300, and 400°C for 48 h in a N 2 gas atmosphere. The results of the XRD for the heat treated samples is in good agreement with the thermogravimetric analysis found in the literature and shows that X-ray powder diffraction can be used as a suitable technique to study the composition and phase diagram of renal calculi.

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Urolithiasis is a metabolic disease, which is characterized by formation of stones (calculi) in urinary tracts, affects a wide sector of population 4-15% approximately (depending on geographical area). The stones composition can be classified into two parts, an organic matrix and biominerals. Stones are often heterogeneous, containing mainly oxalate, phosphate, and uric acid crystals. The analysis of the mineral composition of urinary stones is an important requirement for a successful management of the disease, which implies not only a proper evaluation and treatment, but also prophylaxis to prevent recurrence. In this work we characterized the mineral composition of human urinary stones from Rio de Janeiro residents using Synchrotron X-ray diffraction (XRD) performed on the regions of interest (ROI) predetermined by microtomography. The results have shown that the calculi are mixed and comprising calcium oxalate monohydrate, calcium oxalate dihydrate, hydroxyapatite and struvite. In this paper, we highlight the presence of struvite, also known as infection stone. The incidence of struvite might be due to the samples being from patients under hospital treatment and / or a particular feature of the residents of Rio de Janeiro.

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