Ca2C2O4

Calcium oxalate, with the chemical formula Ca2C2O4, is an inorganic chemical compound. It is the calcium salt of oxalic acid. In its pure form, calcium oxalate is a white, odorless, crystalline solid. It is sparingly soluble in water, and its solubility decreases with increasing temperature.

Calcium oxalate exists in several hydrated forms, with monohydrate (CaC2O4·H2O) and dihydrate (CaC2O4·2H2O) being the most common. The anhydrous form (CaC2O4) is also known. The precise crystalline structure and properties can vary depending on the hydration state and the conditions under which it is formed.

This compound is naturally occurring and can be found in plants, particularly in the leaves and stems of many species, such as spinach, rhubarb, and sorrel. In animals, including humans, calcium oxalate is a major component of kidney stones, which can form when calcium and oxalate levels in the urine are high.

Industrially, calcium oxalate is produced by the reaction of a soluble calcium salt, such as calcium chloride, with a soluble oxalate salt, such as sodium oxalate. It finds some applications as a pigment, in the preparation of other calcium compounds, and in certain analytical chemistry procedures. Due to its insolubility, it is also used as a clarifying agent in some industrial processes.