|Jmol-3D images||Image 1|
|Molar mass||128.097 g/mol, anhydrous
146.112 g/mol, monohydrate
|Density||2.12 g/cm3, anhydrous
2.12 g/cm3, monohydrate
200 °C, decomposes (monohydrate)
|Solubility in water||6.7 mg/L (20 °C)|
|Other cations||Beryllium oxalate
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Calcium oxalate (in archaic terminology, oxalate of lime) is a chemical compound that forms envelope-shaped crystals, known in plants as raphides. A major constituent of human kidney stones, the chemical is also found in beerstone, a scale that forms on containers used in breweries. Its chemical formula is CaC2O4 or Ca (COO)2.
Many plants accumulate calcium oxalate as it has been reported in over 1000 different genera of plants . The calcium oxalate accumulation is linked to the detoxification of calcium (Ca2+) in the plant.
Calcium oxalate is a poisonous substance that can produce sores and numbing on ingestion and could even be fatal.
The poisonous plant dumb cane (Dieffenbachia) contains the substance and on ingestion can prevent speech and be suffocating. It is also found in rhubarb (in large quantities in the leaves) and in species of Oxalis, Araceae, taro, kiwifruit, tea leaves, agaves, and Alocasia and in spinach in varying amounts. Insoluble calcium oxalate crystals are found in plant stems, roots, and leaves and produced in idioblasts.
Calcium oxalate, as 'beerstone', is a brownish precipitate that tends to accumulate within vats, barrels and other containers used in the brewing of beer. If not completely removed in a cleaning process, beerstone will leave an unsanitary surface that can harbour microorganisms. Beerstone is composed of calcium and magnesium salts and various organic compounds left over from the brewing process; it promotes the growth of unwanted microorganisms that can adversely affect or even ruin the flavor of a batch of beer.
Most crystals look like a 6 sided prism and often look like a pointed picket from a wooden fence. More than 90% of the crystals in a urine sediment will have this type of morphology. These other shapes are less common than the 6 sided prism, however it is important to be able to quickly identify them in case of emergency.
Urine microscopy showing calcium oxalate crystals in the urine. Of special interest is the 6 sided three-dimensional morphology which appears as if viewing the top of a picket fence in this image.
Effects of ingestion 
Even a small dose of calcium oxalate is enough to cause intense sensations of burning in the mouth and throat, swelling, and choking that could last for up to two weeks. In greater doses it can cause severe digestive upset, breathing difficulties, coma or even death. Recovery from severe oxalate poisoning is possible, but permanent liver and kidney damage may have occurred.
The stalks of plants in the Dieffenbachia genus produce the most severe oxalate reactions. The needle-like oxalate crystals produce pain and swelling when they contact lips, tongue, oral mucosa, conjunctiva, or skin. Edema primarily is due to direct trauma from the needle-like crystals and, to a lesser extent, by other plant toxins (e.g., bradykinins, enzymes).
Depending on the plant ingested, mild (Elephant Ear Colocasia esculenta) to more severe (Jack in the Pulpit, Arisaema) can cause compromised airways. One bite on the Arisaema seed pod will result in immediate swelling and burning. It will take over 12 hours for the swelling to subside.
Medication administered at the emergency room may include diphenhydramine, epinephrine, or famotidine, all intravenously. Although this most likely will be a localized reaction, it will be treated by the ER as an anaphylactic reaction.
Calcium oxalate is used in the manufacture of ceramic glazes.
- Francesci, V.R.; Nakata (2005). "Calcium oxalate in plants: formation and function.". Annu Rev Plant Biol (56): 41–71.
- Martin, G; Matteo Guggiari, Daniel Bravo, Jakob Zopfi, Guillaume Cailleau, Michel Aragno, Daniel Job, Eric Verrecchia and Pilar Junier (2012). "Fungi, bacteria and soil pH: the oxalate–carbonate pathway as a model for metabolic interaction". Environmental Microbiology 14 (11): 2960–2970.
- Johnson, Dana (23 March 1998). "Removing Beerstone". Modern Brewery Age. Birko Corporation R&D. Retrieved 2007-08-06.
- "Clinical Pathology of Ethylene Glycol Toxicosis". Archived from the original on 2 May 2012. Retrieved 2012-05-17..
- Outbreak of Food-borne Illness Associated with Plant Material Containing Raphides. Informa Healthcare.
- "CALCIUM OXALATE HUMMEL CROTON". Hummel Croton Inc. Retrieved 2012-05-02.