Calcium oxalate (in archaic terminology, oxalate of lime) is a

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quantitie ...

oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and formula . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name comes from the fact that early inve ...

with the chemical formula . It forms hydrates , where ''n'' varies from 1 to 3. Anhydrous and all hydrated forms are colorless or white. The monohydrate occurs naturally as the mineral

whewellite Whewellite is a mineral, hydrated calcium oxalate, formula Ca C2 O4· H2O. Because of its organic content it is thought to have an indirect biological origin; this hypothesis is supported by its presence in coal and sedimentary nodules. Howev ...

, forming envelope-shaped crystals, known in plants as

raphide Raphides (pronounced /ˈræfɪˌdiz/, singular raphide /ˈreɪfʌɪd/ or raphis) are needle-shaped crystals of calcium oxalate monohydrate (prismatic monoclinic crystals) or calcium carbonate as aragonite ( dipyramidal orthorhombic crystals), fo ...

s. The two rarer hydrates are dihydrate , which occurs naturally as the mineral

weddellite Weddellite ( Ca C2 O4·2 H2O) is a mineral form of calcium oxalate named for occurrences of millimeter-sized crystals found in bottom sediments of the Weddell Sea, off Antarctica. Occasionally, weddellite partially dehydrates to whewellite, formi ...

, and trihydrate , which occurs naturally as the mineral caoxite, are also recognized. Some foods have high quantities of calcium oxalates and can produce sores and numbing on ingestion and may even be fatal. Tribes with diets that depend highly on fruits and vegetables high in calcium oxalate, such as in

Micronesia Micronesia (, ) is a subregion of Oceania, consisting of about 2,000 small islands in the western Pacific Ocean. It has a close shared cultural history with three other island regions: the Philippines to the west, Polynesia to the east, and ...

, reduce the level of it by boiling and cooking them. They are a constituent in 76% of human

kidney stones Kidney stone disease, also known as nephrolithiasis or urolithiasis, is a crystallopathy where a solid piece of material (kidney stone) develops in the urinary tract. Kidney stones typically form in the kidney and leave the body in the urine s ...

. Calcium oxalate is also found in beerstone, a scale that forms on containers used in

breweries A brewery or brewing company is a business that makes and sells beer. The place at which beer is commercially made is either called a brewery or a beerhouse, where distinct sets of brewing equipment are called plant. The commercial brewing of bee ...

Occurrence

Many plants accumulate calcium oxalate as it has been reported in more than 1000 different genera of plants. The calcium oxalate accumulation is linked to the detoxification of calcium () in the plant. Upon decomposition, the calcium oxalate is oxidised by bacteria, fungi, or wildfire to produce the soil nutrient Calcium carbonate. The

poison Poison is a chemical substance that has a detrimental effect to life. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figuratively, with a broa ...

ous plant dumb cane (''

Dieffenbachia ''Dieffenbachia'' , commonly known as dumb cane or leopard lily, is a genus of tropical flowering plants in the family Araceae. It is native to the New World Tropics from Mexico and the West Indies south to Argentina. Some species are widely cul ...

'') contains the substance and on ingestion can prevent speech and be suffocating. It is also found in

sorrel Sorrel (''Rumex acetosa''), also called common sorrel or garden sorrel, is a perennial herbaceous plant in the family Polygonaceae. Other names for sorrel include spinach dock and narrow-leaved dock ('dock' being a common name for the genus '' ...

rhubarb Rhubarb is the fleshy, edible stalks ( petioles) of species and hybrids (culinary rhubarb) of ''Rheum'' in the family Polygonaceae, which are cooked and used for food. The whole plant – a herbaceous perennial growing from short, thick rhizo ...

(in large quantities in the leaves),

cinnamon Cinnamon is a spice obtained from the inner bark of several tree species from the genus ''Cinnamomum''. Cinnamon is used mainly as an aromatic condiment and flavouring additive in a wide variety of cuisines, sweet and savoury dishes, breakfa ...

turmeric Turmeric () is a flowering plant, ''Curcuma longa'' (), of the ginger family, Zingiberaceae, the rhizomes of which are used in cooking. The plant is a perennial, rhizomatous, herbaceous plant native to the Indian subcontinent and Southeast Asi ...

and in species of ''

Oxalis ''Oxalis'' ( (American English) or (British English)) is a large genus of flowering plants in the wood-sorrel family Oxalidaceae, comprising over 550 species. The genus occurs throughout most of the world, except for the Polar region, polar are ...

'',

Araceae The Araceae are a family of monocotyledonous flowering plants in which flowers are borne on a type of inflorescence called a spadix. The spadix is usually accompanied by, and sometimes partially enclosed in, a spathe (or leaf-like bract). Also ...

, ''

Arum italicum ''Arum italicum'' is a species of flowering herbaceous perennial plant in the family Araceae, also known as Italian arum and Italian lords-and-ladies.

'',

taro Taro () (''Colocasia esculenta)'' is a root vegetable. It is the most widely cultivated species of several plants in the family Araceae that are used as vegetables for their corms, leaves, and petioles. Taro corms are a food staple in Africa ...

kiwifruit Kiwifruit (often shortened to kiwi in North American, British and continental European English) or Chinese gooseberry is the edible berry of several species of woody vine A vine (Latin ''vīnea'' "grapevine", "vineyard", from ''vīnum'' ...

, tea leaves,

agave ''Agave'' (; ; ) is a genus of monocots native to the hot and arid regions of the Americas and the Caribbean, although some ''Agave'' species are also native to tropical areas of North America, such as Mexico. The genus is primarily known for ...

s, Virginia creeper (''

Parthenocissus quinquefolia ''Parthenocissus quinquefolia'', known as Virginia creeper, Victoria creeper, five-leaved ivy, or five-finger, is a species of flowering vine in the grape family, Vitaceae. It is native to eastern and central North America, from southeastern Ca ...

''), and ''

Alocasia ''Alocasia'' is a genus of rhizomatous or tuberous, broad-leaved, perennial, flowering plants from the family Araceae. There are about 90 accepted species native to tropical and subtropical Asia and eastern Australia. Around the world, many growe ...

'' and in

spinach Spinach (''Spinacia oleracea'') is a leafy green flowering plant native to central and western Asia. It is of the order Caryophyllales, family Amaranthaceae, subfamily Chenopodioideae. Its leaves are a common edible vegetable consumed either f ...

in varying amounts. Plants of the genus ''

Philodendron ''Philodendron'' is a large genus of flowering plants in the family (biology), family Araceae. , the World Checklist of Selected Plant Families accepted 489 species; other sources accept different numbers. Regardless of number of species, the gen ...

'' contain enough calcium oxalate that consumption of parts of the plant can result in uncomfortable symptoms. Insoluble calcium oxalate crystals are found in plant stems, roots, and leaves and produced in

idioblast An idioblast is an isolated plant cell that differs from neighboring tissues. They have various functions such as storage of reserves, excretory materials, pigments, and minerals. They could contain oil, latex, gum, resin, tannin or pigments etc. ...

Vanilla Vanilla is a spice derived from orchids of the genus ''Vanilla (genus), Vanilla'', primarily obtained from pods of the Mexican species, flat-leaved vanilla (''Vanilla planifolia, V. planifolia''). Pollination is required to make the p ...

plants exude calcium oxalates upon harvest of the orchid seed pods and may cause

contact dermatitis Contact dermatitis is a type of acute or chronic inflammation of the skin caused by exposure to chemical or physical agents. Symptoms of contact dermatitis can include itchy or dry skin, a red rash, bumps, blisters, or swelling. These rashes are ...

. 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 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 flavour of a batch of beer. Calcium oxalate crystals in the urine are the most common constituent of human

, and calcium oxalate crystal formation is also one of the toxic effects of

ethylene glycol poisoning Ethylene glycol poisoning is poisoning caused by drinking ethylene glycol. Early symptoms include Substance intoxication, intoxication, vomiting and abdominal pain. Later symptoms may include a decreased level of consciousness, headache, and seiz ...

Chemical properties

Calcium oxalate is a combination of calcium ions and the conjugate base of

, the oxalate anion. Its aqueous solutions are slightly basic because of the basicity of the oxalate ion. The basicity of calcium oxalate is weaker than that of

sodium oxalate Sodium oxalate, or disodium oxalate, is the sodium salt of oxalic acid with the formula Na2C2O4. It is a white, crystalline, odorless solid, that decomposes above 290 °C. Disodium oxalate can act as a reducing agent, and it may be used as a pri ...

, due to its lower solubility in water. Solid calcium oxalate hydrate has been characterized by

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

. It is a

coordination polymer A coordination polymer is an inorganic or organometallic polymer structure containing metal cation centers linked by ligands. More formally a coordination polymer is a coordination compound with repeating coordination entities extending in 1, 2, o ...

. featuring planar oxalate anions linked to calcium, which also has water

ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...

Medical significance

Calcium oxalate can produce sores and numbing on ingestion and may even be fatal.

Morphology and diagnosis

The monohydrate and dihydrate can be distinguished by the shape of the respective crystals. * Calcium oxalate ''dihydrate'' crystals are

octahedral In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...

. A large portion of the crystals in a urine sediment will have this type of morphology, as they can grow at any pH and naturally occur in normal urine. * Calcium oxalate ''monohydrate'' crystals vary in shape, and can be shaped like dumbbells, spindles, ovals, or picket fences, the last of which is most commonly seen due to

. File:Calcium oxalate crystals in urine.jpg, Urine microscopy showing calcium oxalate crystals in the urine. The

crystal morphology is clearly visible. File:Calcium oxalate crystals (urine) - kalsiyum oksalat kristalleri (idrar) - 01.png, Urine microscopy showing a ''calcium oxalate monohydrate'' crystal (dumbbell shaped) and a ''calcium oxalate dihydrate'' crystal (envelope shaped) along with several erythrocytes. File:Calcium oxalate crystals (urine) - kalsiyum oksalat kristalleri (idrar) - 02.png, Urine microscopy showing several ''calcium oxalate monohydrate'' crystals (dumbbell shaped, some of them clumped) and a ''calcium oxalate dihydrate'' crystal (envelope shaped) along with several erythrocytes. File:Calcium Oxalate Detail.png, Urinary sediment showing several calcium oxalate crystals. 40X

Kidney stones

About 76% of kidney stones are partially or entirely of the calcium oxalate type. They form when urine is persistently saturated with calcium and oxalate. Between 1% and 15% of people globally are affected by kidney stones at some point. In 2015, they caused about 16,000 deaths worldwide. Some of the oxalate in urine is produced by the body. Calcium and oxalate in the diet play a part but are not the only factors that affect the formation of calcium oxalate stones. Dietary oxalate is an organic ion found in many vegetables, fruits, and nuts. Calcium from bone may also play a role in kidney stone formation. In one study of modulators of calcium oxalate crystallization in urine, magnesium-

alkali citrate Alkali citrate (also known as alkaline citrate) is an inhibitor of kidney stones. It is used to increase urine citrate levels - this prevents calcium oxalate stones by binding to calcium and inhibiting its binding to oxalate. It is also used to in ...

was shown to inhibit CaOx (calcium oxalate) crystallization, “probably via actions of the citrate, but not the Mg.” This was in comparison to magnesium, citrate, and magnesium citrate. Currently the preparation of magnesium-potassium citrate that was used in one positive study is not available in the United States.

Industrial applications

Calcium oxalate is used in the manufacture of ceramic glazes.

References

{{DEFAULTSORT:Calcium Oxalate Oxalates Calcium compounds Kidney