Calcium oxalate is a chemical compound with the chemical formula CaC2O4. It is an ionic compound composed of calcium (Ca) cations and oxalate (C2O4^2-) anions. Calcium oxalate occurs naturally in various forms and is widely distributed in plants, animals, and minerals.

Here are some key points about calcium oxalate:

1. Structure: Calcium oxalate has an ionic crystal structure, consisting of one calcium cation (Ca^2+) and one oxalate anion (C2O4^2-) held together by ionic bonds.
2. Physical Properties: Calcium oxalate exists in different crystal forms, including monohydrate and dihydrate. The monohydrate form is called whewellite, while the dihydrate form is known as weddellite. Both forms are white, odorless solids.
3. Occurrence: Calcium oxalate is commonly found in many plants, where it often accumulates as crystals known as raphides. It can also be found in certain minerals and is a component of some kidney stones in humans.
4. Formation: Calcium oxalate can form when calcium ions (Ca^2+) react with oxalate ions (C2O4^2-) in solution.
5. Uses: Calcium oxalate has limited practical applications. It is primarily used in research and laboratory settings as a source of calcium cations and oxalate anions in various chemical reactions.
6. Toxicity: Calcium oxalate is generally considered to be low in toxicity when ingested in small amounts. However, large quantities can cause health issues, and kidney stones composed of calcium oxalate can lead to kidney-related problems.
7. Environmental Concerns: Calcium oxalate is not considered to be harmful to the environment when used appropriately and in accordance with regulations.

In plants, calcium oxalate serves various functions, including storage of excess calcium and acting as a defense mechanism against herbivores due to its sharp crystals. In humans, calcium oxalate kidney stones can form when there is an excessive concentration of oxalate in the urine.

As with any chemical compound, proper handling and disposal practices are essential to prevent environmental contamination and to ensure safety when using calcium oxalate. Additionally, in the case of kidney stones, it’s important to follow appropriate medical advice and treatments to manage and prevent complications.