Solubility stone-forming substances

Most kidney stones are composed of calcium oxalate, an insoluble substance that forms when soluble calcium compounds combine with oxalate in the kidneys. We get calcium from our diets. We get most of our oxalate the same way, although some can form when we consume excessive amounts of vitamin C. 

In the chapter opening, we mentioned that calcium oxalate precipitates to form kidney stones. The same salt would precipitate in the body if oxalic acid (a poison) were accidentally ingested, because ion is present in the blood. (See Figure 18.3 for another example of a precipitation.) To understand processes such as these, you must understand the conditions under which precipitation occurs. Precipitation is merely another way of looking at a solubility equilibrium. Rather than ask how much of a substance will dissolve in a solution, you ask Will precipitation occur for given starting ion concentrations ... 

---