Summary: Today I want to talk about some of the youngest minerals on earth – kidney stones. Some might argue whether these should be considered minerals at all, since part of the definition of a mineral is other than man-made, but that’s usually phrased as “naturally occurring” and these mineral deposits really are natural, even if they are not welcome. My first professional job was analyzing kidney stones. My mineralogy professor, Carl Beck at Indiana University, had died, and his wife asked me, his only grad student, if I would continue the analytical business he had been operating. I said yes, setting out on a four-year, 20,000-kidney-stone start to my geological career. First, please accept this disclaimer. I am not a medical doctor. I’m not even a geological doctor. So don’t take anything I say as medical advice. Apatite is a common mineral in nature. Chemically it is a complex calcium phosphate with attached molecules of hydroxyl (OH), fluorine (F), and sometimes other elements. Apatite is the fundamental mineral component in bones and teeth, and when apatite has fluorine in its crystal structure, it is stronger. This is why fluorine is added to water and toothpaste. In kidney stones, carbonate (CO3) substitutes for some of the phosphate, making a mineral that is relatively poorly crystallized. Its formula in kidney stones is usually given as Ca5(PO4,CO3)3(F, OH, Cl). Well-crystallized or not, apatite often forms the nucleus upon which other urinary minerals are deposited. It usually occurs as a white powdery mineral deposit, one of the most common components of kidney stones. Two minerals that are really common in human urinary stones but that are exceedingly rare in nature are whewellite and weddellite, calcium oxalates. Oxalate is C2O4, not too different chemically from carbonate, CO3, the common constituent of limestone. Whewellite (CaC2O4.H2O) is known to occur in septarian nodules from marine shale near Havre, Montana, with golden calcite at Custer, South Dakota, and as a fault filling with celestite near Moab, Utah. It is found in hydrothermal veins with calcite and silver in Europe, and it often occurs in association with carbonaceous materials like coal, particularly in Saxony, the former Czechoslovakia, and Alsace. Whewellite was named for William Whewell, an English poet, mathematician, and naturalist who is credited with the first use of the word ‘scientist,’ in 1833. It is one of the most common kidney stone minerals, where it typically occurs as small, smooth, botryoidal – which means like a mass of grapes – to globular yellow-green to brown, radially fibrous crystals. Whewellite stones larger than ½ inch across are quite unusual. Often whewellite is deposited upon a tiny nucleus of apatite, which may form as build-ups on the tips of tiny papillae in the kidney. Those papillae are little points where ducts convey the urine produced by the kidney into the open part of the kidney. Weddellite, CaC2O4.2H2O, was named for occurrences of millimeter-sized crystals found in bottom sediments of the Weddell Sea, off Antarctica. Unfortunately the sharp yellow crystals that urinary weddellite forms are often much larger than that, and they are frequently the cause of the pain experienced in passing a kidney stone. Rarely, weddellite crystals may occur that are nearly a half inch on an edge, but most are somewhat smaller. The yellow crystals are commonly deposited upon the outer surface of a smooth whewellite stone. Like whewellite, weddellite is a calcium oxalate. They differ in the amount of water that is included in their crystal structures, and this gives them very different crystal habits. Occasionally, weddellite partially dehydrates to whewellite, forming excellent pseudomorphs of grainy whewellite after weddellite's short tetragonal dipyramids. Together, apatite, whewellite, and weddellite are probably the most common urinary stones. Struvite is a hydrous magnesium ammonium phosphate, Mg(NH4)(PO4).6H2O, that forms
