Among the mineral phases composing human kidney stones, spherulites of whewellite, i.e., calcium oxalate monohydrate (CaC2O4-H2O), are the most widespread. The composition and morphology, especially the internal structure of these aggregates and their formation conditions have been studied using mineralogical tools. The stones result from heterogeneous nucleation and growth under conditions of high supersaturation existing in the kidney. In most cases nuclei of two types - calcium phosphates + organic matrix, or CaC2O4·H2O microcrystallites - have been distinguished, although whewellite crystallization on seeds of uric acid are also noted. The spherulitic aggregates have a fine-fibered structure complicated by helicoidal torsion, which accounts for their abnormal strength and resistance to disintegration. These distinctive physical characteristics of CaC2O4·H2O spherulitic aggregates requires high-energy impulses extracorporeal shock-wave lithotripsy (ESWL) for their disintegration and removal from the body, although it is not an optimal method for the patient.

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