Weddellite (
CaCalcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust...
CCarbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
2OOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
4·2
H2OWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
) is a mineral form of
calcium oxalateCalcium oxalate is a chemical compound that forms needle-shaped crystals. Its chemical formula is CaC
2O
4 or Ca
2.-Occurrence:...
named for occurrences of millimeter-sized crystals found in bottom sediments of the
Weddell SeaThe Weddell Sea is part of the Southern Ocean. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. Much of the southern part of the sea, up to Elephant Island, is permanent ice, the Filchner-Ronne Ice Shelf...
, off
Antarctica| style="border-top:solid 1px #ccd2d9; padding:0.4em 1em 0.4em 0; vertical-align:top;" | 14,000,000 km
2 280,000 km
2 13,720,000 km
2 |-! style="border-top: solid 1px #ccd2d9; padding: 0.4em 1em 0.4em 0; vertical-align: top;...
. Occasionally, weddellite partially dehydrates to
whewelliteWhewellite is a mineral, hydrated calcium oxalate, formula CaC
2O
4·H
2O. Because of its organic content it is thought to have an indirect biological origin and this is supported by it being found in coal and sedimentary nodules. However, it has also been found...
, forming excellent
pseudomorphIn mineralogy, a pseudomorph is a mineral or mineral compound that appears in an untypical form , resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by another...
s of grainy whewellite after weddellite's short tetragonal dipyramids.
Structural properties
The weddellite or
calciumCalcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust...
oxalateAn oxalate is the deprotonated, charged form of oxalic acid or an ester of oxalic acid. The oxalate anion has the chemical formula C2O42−, also written...
di-hydrate crystallizes in the tetragonal system. The classic crystal shape is the eight-face bi-pyramid. In bright field microscopy, the weddellite crystals are recognized easily by their shape that reminds a mail envelope. More complex shapes of weddellite are possible. The dumbbell shape is not rare. The former has no precise angles or sides. This form is, in reality, a microcrystalline agglomerate that takes the shape of a biconcave disc. Weddellite crystals are poorly birefringent and do not show any interference pattern under polarized light.
Biological role
Weddellite crystals are usually of little clinical value. Many specimens develop weddellite crystals on standing. Together,
apatiteApatite is a group of phosphate minerals, usually referring to hydroxyapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH
−, F
−, Cl
− or...
,
whewelliteWhewellite is a mineral, hydrated calcium oxalate, formula CaC
2O
4·H
2O. Because of its organic content it is thought to have an indirect biological origin and this is supported by it being found in coal and sedimentary nodules. However, it has also been found...
, and weddellite are probably the most common urinary stones.
Varieties and related minerals
Natroxalate,
WhewelliteWhewellite is a mineral, hydrated calcium oxalate, formula CaC
2O
4·H
2O. Because of its organic content it is thought to have an indirect biological origin and this is supported by it being found in coal and sedimentary nodules. However, it has also been found...
, Caoxite, Novgorodovaite, Oxammite, Glushinskite, Humboldtine, Minguzzite,
ZhemchuzhnikoviteZhemchuzhnikovite is a mineral of organic origin; formula NaMgC2O4.8H2O. It forms smokey green crystals with a vitreous lustre and is found in Russian coal mines. It is named after Yury Zhemchuzhnikov , a Russian clay mineralogist.-References:**...
, Stepanovite,
MoolooiteMoolooite is a rare blue-green mineral with the formula Cu++·n . It was discovered by Richard M Clarke and Ian R Williams in Bunbury Well, Mooloo Downs station, Murchison, Western Australia in 1986...
, Wheatleyite, Coskrenite