Calcium oxalate

Calcium oxalate is a chemical compound. It is the calcium salt of oxalic acid. It has the chemical formula CaC2O4 or Ca(COO)2. It can be found as a dry form, or one of several hydrates.

Calcium oxalate can be found as both a mineral and in living things. Plants can make calcium oxalate out of extra calcium from the soil. In humans, it is the most common chemical in kidney stones.

Occurrence

Calcium oxalate is most commonly found as the monohydrate, Ca(COO)2·H2O. As a mineral, this is called whewellite. There are also dihydrate (Ca(COO)2·2 H2O) and trihydrate (Ca(COO)2·3 H2O) forms.

Calcium oxalate occurs naturally in many plants as a way of storing extra calcium. In some species, like pineapples, it forms sharp crystals called raphides. Along with the enzyme bromelain, these crystals may help protect the plants from herbivores.[1] Calcium oxalate is the most common oxalate found in lichens.[2]

Calcium oxalate is oxidised into calcium carbonate by living things, especially bacteria.[3]

Human health

Having too much oxalate in the body is called hyperoxaluria, and can lead to a kidney failure called oxalosis.[4]

Oxalate is absorbed by water during cooking, with boiling being the most effective.[5]

Calcium oxalate in urine can crystallise into kidney stones. Calcium oxalate is a metabolite of ethylene glycol and is involved in ethylene glycol poisoning.[6]

Sources

  1. ↑ Haleh Cohn (2023-05-26). "Why Does Pineapple Make Your Mouth Tickle?". McGill University Press. Retrieved 2025-08-05.
  2. ↑ Krajanová, Viktória (2023). "Discoveries and identification methods of metal oxalates in lichens and their mineral associations: A review of past studies and analytical options for lichenologists". Fungal Biology Reviews. 43 100287. Bibcode:2023FunBR..4300287K. doi:10.1016/j.fbr.2022.09.003.
  3. ↑ Cailleau, Guillaume; Mota, Matteo; Bindschedler, Saskia; Junier, Pilar; Verrecchia, Eric P. (2014). "Detection of active oxalate–carbonate pathway ecosystems in the Amazon Basin: Global implications of a natural potential C sink". Catena. 116: 132–141. Bibcode:2014Caten.116..132C. doi:10.1016/j.catena.2013.12.017.
  4. ↑ "Hyperoxaluria and oxalosis". Mayo Clinic. Retrieved 2025-08-05.
  5. ↑ Chai, Weiwen; Liebman, Michael (2005). "Effect of Different Cooking Methods on Vegetable Oxalate Content". Journal of Agricultural and Food Chemistry. 53 (8): 3027–3030. Bibcode:2005JAFC...53.3027C. doi:10.1021/jf048128d. PMID 15826055.
  6. ↑ Pomara, Cristoforo; Fiore, Carmela; d'Errico, Stefano; Riezzo, Irene; Fineschi, Vittorio (2008). "Calcium oxalate crystals in acute ethylene glycol poisoning: A confocal laser scanning microscope study in a fatal case". Clinical Toxicology. 46 (4): 322–324. doi:10.1080/15563650701419011. PMID 18363130.
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