Epitaxial Relationships in Urolithiasis: The Brushite—Whewellite System

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Abstract
Whewellite (calcium oxalate monohydrate) crystals induced epitaxially the heterogeneous nucleation of brushite (calcium monohydrogen phosphate dihydrate) from its metastable supersaturated solution in approximately 1/4 of the time required for spontaneous precipitation in the absence of added nucleating agents. Scanning electron microscopic observation of the crystalline phase showed brushite crystals originating from the whewellite seed crystals. Crystal growth, upon nucleation, proceeded rapidly, and the metastable solutions quickly approached saturation. Brushite crystals also induced the precipitation of calcium oxalate crystals in about 1/4 of the time required for spontaneous precipitation; however, the rate of crystal growth was considerably slower. In support of the chemical data, scanning electron micrographs showed few crystals of calcium oxalate nucleated on the surface of the brushite seed. The results provide some insight into the cause of stones containing calcium oxalate or calcium phosphate (or both), which form in the normally acid environment of human urine.